We were trying to make airplane-sized birds, which don't exist in nature for a variety of very good reasons.

Equally, our materials science wasn't good enough for flapping wings at the time.

I expect to see flapping wing designs appearing in micro-flyers within a decade. At the insect scale they're really useful:

http://www.epsrc.ac.uk/newsevents/casestudies/2011/Pages/Tin...