Fortunately, the reason you offer for the lack of Disgaea 3 and 4 ports lacks substance due to the existence of their Vita ports, programmed for a much more manageable ARM-based environment. I agree with @RedMattis about the likely real reason. Give it a few years.
Jo, if I tell you the reason why D3/4 and/or DS arent on PC and you are satisfied with the answer to at least one of them... Will you make a chapter(s) on Angie and Victoire at the beach wearing sexy bikini's while being very intimate/lewd (I'll leave that up to your imagination)? Summer is upon us.
Demon's Souls is a Sony IP as far as ownership is concerned which is why it can never be ported. Same deal with Bloodborne. Not sure the proper terminology, but basically it will never be ported unless Sony ports it.
PS3 emulation is a pain in the arse while PS4 emulation is a breeze
there is a reason why the PCSX4 (PS4 emulator) is booming while the RPCS3 (PS3 emulator) is struggling to run uncharted or TLOU with decent frame rate
They're already porting 5 to the Switch and stuff, so why wouldn't they use their most current version? They already put the work into it? Besides its not like you can't get all the old cast already in 5 lol
Disgaea games are pretty similar. I don't think releasing several of them back-to-back within a short time is a good idea. Besides, 1, 2 and 5 are probably the most iconic ones. I do miss the giant monsters from 4 though.