There's also the fact that there is no standard disc wheel, companies are all setting their own standards for disc size, axle, etc...until those aspects are worked out, the neutral service for a race might not have the wheel you need, so if your team car isn't nearby, you're stuck standing on the side of the road.

At this point, I think many of the pros aren't interested in them because they can stop just fine with what they already have. I've yet to see anyone not be able to stop and fly off the side of the road in a race.

We basically have a technology that seems helpful to your everyday rider, yet a lot of disinterest from the professionals. I personally think disc will stick around on gravel/adventure bikes, but will fade from road bikes over time. Of course, gravel/adventure bikes are quickly becoming the rage even on the street because they allow for wider tires, so it'll all even out in the wash.