It would be a nightmare for attractions CMs. If they made everyone scan a ticket or MB at entrances, you're looking at longer standby waits - look at how the FP+ lines back up from the touchpoints. And then there's the people who'd try to sneak into the attractions lines, because rules just don't apply to them.
It would also be a pain for CMs selling tickets, to try to explain to guests who don't speak much, if any English that the cheaper price they saw doesn't include the rides.
And then there's the poor CMs at Guest Relations, getting to deal with all the complaints from people who unknowingly just buy the cheapest ticket and get mad when they can't go on rides. (The website can explain it all it wants - some people just don't read what they're buying.)
At the end of the day, the parks are meant to be whole attractions in and of themselves - rides, shows, nighttime entertainment, street entertainment, shopping, dining, and environmental ambiance. Selling a "no rides" ticket would undermine that philosophy, and so I don't think they'll do it - unless someone decides there's a great deal of profit in it, which I don't think is too likely.