The reason is because the fundamental core of Catholicism is that we are One, Holy, Catholic and Apostolic. Unlike most other faiths, the Roman Catholic Church is not run at the local or Diocesan level, it all flows directly from the Holy See, so an action of the type you claim took place at your wedding would be a huge violation of canonical law, of a nature that could have a priest defrocked if it was a systematic behavior. So I just don't think it was likely; it was, however, quite likely that you believed that to be the case, may have even been led to assume that was the case, and that nobody cared to attend your wedding, and that therefore you never knew the difference.
Honestly, I don't care and it's not relevant to me what you believe, but it would be the equivalent of saying that the Hail Mary was said in a Lutheran mass; it is antithetical to the faith, so I just doubt it happened.
Forgive me if I missed a post somewhere on this, but I'm going to point out that permission for an RC church to host the marriage of Catholic non-parishioners may be generally issued by the Local Ordinary; that is, the Bishop of the Diocese. Such permission is given rather frequently, particularly in the case of churches that belong to Religious Orders, and may or may not be associated with a parish. Such facilities are often allowed to offer Sacraments for any member of the Church in good standing who is eligible to participate in the particular rite. They are usually either college churches, oratories, or private chapels. It is called a "general office", and this is spelled out in Canon Law, Can.1111,section 1, and also in Can.1115
http://www.vatican.va/archive/ENG1104/__P40.HTM
Here is an example, from the FAQ's of the St. Francis Xavier College Church at St. Louis University:
Who may be Married at the College Church?
Any baptized Roman Catholic may marry at St. Francis Xavier Church with an ordained priest or deacon to witness the Sacrament of Marriage. Reservations for the church are accepted one year in advance. SLU affiliates (brides or grooms who are SLU alums, students or faculty) are allowed to book a reservation a year in advance in the calendar month in question. The calendar opens on the first working day of the month in question THIS YEAR. All reservations are taken over the phone beginning at 8:30 a.m. that morning. Non-affiliated couples may make their selections beginning at 9:00 a.m. that same morning, once the affiliates have made their selections. Registered, participating and contributing parishioners who have been with us for at least 10 months prior to requesting a date may request a date at any time. The one exception that supersedes all of the above is when a couple needs to contract both the Xavier Grand Ballroom and the Church in order to tie together the wedding. In that case, any date and time is eligible to book, but the Ballroom fees must be paid within 90 days. The fee is the same for anyone reserving the church for a wedding: $900. This fee is for the church alone and does not represent the stipend properly given to the officiating priest or deacon, an amount typically in the $200 range.
This is perfectly legal under Canon law, provided that the church in question has been granted a general office by the local Bishop for the celebration of Marriages. (St. Francis Xavier happens to belong to the Jesuits, but there are at least two other churches within the boundaries of my Archdiocese that may marry out-of-parish Catholics.) The person who actually officiates at the marriage must take responsibility for validating your status to enter into a marriage, but in the case of those who undergo RC Marriage Preparation, that investigation is done by the clergy who oversee the class. If that clergyman signs an affidavit that you have status to marry, then you usually can do so in any Catholic church that holds a general office for marriages.
As you see from the above example, there customarily IS a payment directly to the officiating priest; this is not the donation to the Church that is meant to cover the cost of the use of the building; it is a stipend for his services in performing an extra Mass. (Stipends are also normally given to priests when they perform funerals.) If you want to argue over whether it is a donation or a fee, you are arguing semantics, but I would posit that if a minimum "donation" is required in all cases, then it really isn't all that far out of order to call it a fee, because you will not be getting married there if you don't pay it. Using the term "rent" does rather imply something a bit less solemn, so that term is a bit more iffy.
Here is another example of a mandatory "stipend" for you, from Our Lady of Grace in El Cajon, CA which is a parish church:
DONATION AND STIPEND
In the Diocese of San Diego, the offering made for a wedding is placed in the general operating expenses of the Parish at which the wedding is performed. It is not retained by the presiding celebrant. Extra donation to the priest or deacon is optional. The customary offering for *registered, active parishioners or their children is $200.00. The liturgy and wedding coordinator's fee is $150.00. If altar servers are used, the usual stipend is $5.00 for each server. A $50.00 non-refundable fee is required to hold the date of the wedding. All stipend and fees should be given at least two weeks before the wedding date.
Because of high operating expenses of our church, we are at this time allowing non-parishioners to use our church and asking for a stipend of $500.00 for usage fee; $100.00 non-refundable deposit on the date the wedding date is settled. You will pay the rest ($400.00) two weeks prior to the wedding date. The liturgy and wedding coordinator's fee is $200.00 for non-parishioners.
*REGISTERED: Making regular weekly offering through the envelope
http://www.olg-church.org/wedplan.htm
On the original topic, as to whether or not any member of the public can walk into a wedding in a Catholic Church, Canon Law addresses that:
Can. 1221: Entry to a church at the hours of sacred functions is to be open and free of charge.
http://www.vatican.va/archive/ENG1104/__P4H.HTM
