Property law, not just the contract, controls what may be done with
DVC property and the restrictions that DVC may put on owners. States whose law derives from English common law, which includes Florida and Ohio, have a doctrine known as free alienability of real estate. That means that DVC cannot unreasonably limit the transfer of property rights, which includes the right to rent the use of that property. DVC owners have a legal right to rent the use of their property.
Points are just a symbol of how much DVC real estate each owner has a right to control. No one can use more than their number of points and must follow the rules. Thus, when a person rents points out, they rent no more than the property that they have a right to control. They have not taken away from anyone else.
Whether you get money when you rent points or the love and kisses of your relatives, you are receiving something of value. It does not matter what you receive for the transfer. Whether you use points by occupying the unit yourself, give them away, or rent them, you still are using your amount of property right.
Disney is limited by property law when it comes to controlling a member's right to rent. DVC can state that points are not for business purpose, but exactly what that means probably can only be determined in a court. It cannot mean that a person cannot rent points. For a parallel example, even though a person's apartment lease may say no subleasing, a court (in Ohio and most common law states) will interpret it to mean "no subleasing without approval of the landlord and that approval cannot be unreasonably withheld." That means that landlord can only apply the same standards to a sublease that he/she applies to new renters.
So, even though some would want to leave the points unused when a member cannot personally use them, it is an inefficient use of resources and property. Common law upholds the right to rent out the use of property, Disney knows this, and the rules and contract reflect this.