"there are a whole bunch of series yet not a lot 
of cels..what happen to them..."

Dunno if you meant just the Street Fighter 
variations, or cels in general, but in general, 
there are lots of reasons you might not see cels 
from a given anime:

-The cels might not have ever been officially 
released to the public (Eva)
-There might not be cels at all (anything Toei's 
done recently, like the Mahou Tsukai Tai TV 
series, Kaito Jeanne, or the new Sol Bianca OAV)
-The cels might have been in limited release, but 
the show was popular enough in Japan that 
collectors there snagged them before the cels 
could make it overseas (think any OP or ED 
sequence)

For Street Fighter, I don't know exactly, but I'm 
guessing the show's cels weren't released--very 
frequently video game tie-in stuff can't be 
released because of wacky merchandising agreements 
or whatever (like why Sakura Wars cels are so hard 
to come by).