it wasn't just the WC series, it was just the whole genre dying out. People just didn't want to fly planes/jets/space fighters for some reason. I think as more and more FPSes (quake, return to castle wolfenstein, halo, etc) came out, they just gradually drew the audience away.
I'm not too sure about a lack of customers. Sims and FPS have co-existed for most of pc gaming history. It seems in the last 10 years a lot of the sim products have been shelved for quicker development arcade stand ins, and shovelware
(sim) Links golf = (arcade) tiger woods
Any hint of a real Flight/space sim and us nerds go crazy until its once again shown to be a consolized hump of turd. (e.g. janes new JASF)
IMHO this also goes for:
A real golf sim (no thanks EA)
A real tactical shooter w coop (Rainbox Six [Rogue Spear type, no this Vegas crap]) , and orig ghost recon)
and
A real flight sim (If one doesn't show up soon, I may end up sending my brother win2k vm and vmplayer, with Jane's anthology already installed) Hell its been so bad I don't think I've bough a flight stick in 5-10 years, I guess I stopped buying them at some point...
I tell you... we had to play our sims uphill, BOTH ways...
and get off my damn lawn...