So? You want to limit it to buses fine. The bottom line then is from the time they started to have buses to parks they've had buses between parks. So where is your disconnect here?
And the bigger point is they have always gotten you between parks SOME how. Sure, the OP asked about buses but sometimes there are other ways between the parks and heaves if your only goal is to get between parks then why on earth does the method Disney offers you to use to get there matter?
They have had buses from the HOTELS to the parks for a long time much before they started to offer park to park buses. Initially, they did not have buses between parks. I remember back in the day before the internet, there was Usenet, where there were discussions about how to get to between parks. For buses you had to get to the TTC, to a hotel, or Lake Buena Vista (nee, downtown Disney, nee Disney Springs) and then transfer to the a bus heading to the other park.
It doesn't matter to me how people get from park to park. Again you asked about the rumor that you couldn't get from park to park by BUS. As I stated before, because for a period of time you couldn't get from park to park directly. So using your words "this so-called rumor" was not a rumor it was fact.
You are correct, that they always to get you from park to park by some some means, but there was a period of time where you could not go directly from one park to one park by BUS, which was your premise in regards to the "rumor" in your response to the OP.
There was a point of time when you could not get from park to park directly by bus. You would have to utilize some other type of transportation that included a transfer to a bus or vice versa. For MK to Epcot you would use the monorail transferring at the TTC. As someone else pointed out, for a period of time to get between EPCOT Center and MGM Hollywood Studios, you would have to exit out IG and board a tram.
Do you realize when the MK first opened once you arrived at the TTC and purchased your ticket booklets, you actually had three forms of transportation to get from the TTC to the actual entrance of the Magic Kingdom.
1. Monorail
2. Ferry
3. Trams
The drop off location for the trams was roughly where the current bus depot is at the entrance of the Magic Kingdom
If you were a day guest. You would buy your tickets, and if you looked at the price, it was broken down between theme park entry and transportation. As someone else said you would get a coupon in the booklet to turn in to get to the MK from the TTC and back again.
As I stated, as a day guest if you wanted to do additional "touring" you would need to buy an additional "transportation" ticket.
I am thinking the reasoning was the park entry fees went into one bucket in regards to revenues and the parking fees went into the parking revenue bucket. The $2 transportation fees also went into the parking revenue bucket.
This may have been a residual affect, when the
DisneyLAND monorail was actually controlled by Retlaw (i.e. the Disney Family) Disney the corporation would pay the Disney family for people using the Disneyland monorail. Disney, the corporation eventually bought the concession. I don't think the WDW monorail system ever had this set up. But accounting structure may have been a residual affect.