As someone else pointed out in another thread: for any given sport the olympics is just one competition. For it to remain prestigious it needs to have most of the best competitors in each sport competing in it, and for that it needs to stay fairly close to the mainstream format and constraints of each sport.

Single-design classes are standard in sailing, so the olympics uses them also. They are not standard for cycling, and it would be a huge deviation from conventions of competitive cycling for the olympics to demand them.

That doesn't mean they can't or that it wouldn't possibly be worth while. But there are huge costs to doing that, like possibly few or none of the major competitive cyclists competing.