It depends but I don't think a recumbent bike is all that great when climbing or descending. I can't see cyclists wanting a recumbent if there are any significant elevation changes on the course.

Recumbents are beasts of descending. As long as there are no turns. On a straight descent, they'll beat anything without even trying.

We are talking about pro-cycling. The descents in pro tours have _a lot_ of turns.

Flipping over because of hard braking is not something that happens in pro-cycling.

[edit] And yes, for time trials recumbents would be nice, but already time-trial bikes are pretty different and unsafe, I don't think the UCI would allow even more risk.

The view from a recumbent bike becomes highly obstructed when you're riding in a tight peleton. The group road rides that I do don't allow recumbents for safety reasons. Traditional bikes have their dangers but at least your eyes are up higher to allow a good view around other riders.

Maneuverability is important for time trials. Most courses have several tight turns and crashes are common.