There's some serious business competition going on in the fighter world these days, between the MiG-35, JSF, EF2000, F-16 Block 52+, Silent Eagle, Rafale, Super Hornet, Gripen and Su-30MKI.
It's all about, do you want to wait for an expensive 5th generation fighter that will hopefully allow you to dominate the skies, or get a 4.5 generation fighter now that's a lot cheaper than a 5th gen and with only slightly reduced capability?
Part of it I think is based on how urgently a nation thinks its fighters need to be replaced. And the rest is who has the best political/business ties.