Only older games run at 32-bit and with Direct X 9. Most games we see now can run at 64-bit and have Direct X 11 support on them. Additionally, The developers also have to consider the majority of gamers such as making them playable even on low-spec computers to widen their market. Direct X 12 is still very new so its highly likely that newer games a year or two from now will switch over to it.
Only older games run at 32-bit and with Direct X 9. Most games we see now can run at 64-bit and have Direct X 11 support on them. Additionally, The developers also have to consider the majority of gamers such as making them playable even on low-spec computers to widen their market. Direct X 12 is still very new so its highly likely that newer games a year or two from now will switch over to it.
I guess that makes sense, since most of the games I have noticed using dx9 32 bit are games like Borderlands 2 and Crysis 3, which aren't necessarily old, but are still old enough. Thanks!