I've thought of that too. I'm not aware of any such events but I think like you - the races would simply become a long time trial. Most of the key moments in pack bicycle racing involve some kind of sprint. Whether breaking away from the pack, during an extended climb or at the end of the race, somebody jumps up from the saddle in an effort to sprint away. Recumbents simply don't do that very well.

I'm thinking there might be a safety thing too with all those chain wheels sticking out in front but that's another matter.

Every time somebody whines about recumbents not being allowed in UCI racing, I think to myself that it's probably a good thing.