Because most developers in Japan don't care about PC gaming. How very disappointing because PC is better than consoles. I hate to sound like a fanboy but it's the truth.
I agree with earlier posts, Capcom is the devil with their DLC on arrival releases for material that's already on the disc you just bought... I don't have much love over for SEGA as well, their support on Steam is non existent and their ports - with exception for Sonic Transformed - are mostly broken and badly tested.
Screw Capcom. I've lost a lot of faith in them since they shitcanned Mega Man Legends 3, turned Resident Evil into a joke and made Street Fighter X Tekken a half-finished, broken mess. Sega at least are redeeming themselves, even though they C&D'd Streets of Rage Remake and took down Shining Force LPs for no reason.