I wasn't turned down for a card, but I just got a Barnes and Noble MasterCard, and it only has a $500 CL. When I asked why, I was told that it was because I already had plenty of unused credit, and they felt that I didn't need a larger limit, which was fine.
Otherwise, as the others said, mortgage lenders might asked you to reduce your amount of available credit, as they are worried that you might go on a spree and not be able to pay your mortgage, and for scoring purposes, you can get a flag for "too many" accounts. You can also lose points for having too many accounts with balances.
As with everything else in jittery credit times, you just don't want to appear to creditors as if you have too many eggs in the air at once.
* Credit is a wonderful servant, but a terrible master. * Who's the boss --you or your credit?
FICO's: EQ 781 - TU 793 - EX 779 (from PSECU) - Done credit hunting; having fun with credit gardening. - EQ 590 on 5/14/2007