All good points Gsteinb which I agree with. The only thing I'll add is that while there may only be 8 Olympic road slots, there is track, and when we're talking about pros, you have to add CX. How many amateurs are seriously shooting for an Olympic berth or a pro contract? It has to at least be hundreds. Not a trivial number. I think you are looking at the situation primarily from a Masters road lens.
Barriers to entry is kind of a straw man argument. It's real, for sure, but look at triathlon. Much higher barrier to entry even for the hobbyist sprint athlete yet its popularity dwarfs cycling. It's also rife with dopers at all levels, and has a pro carrot.