It's about artistic integrity, if a writer cannot respect the established lore and adhere to it then why the hell should his/her work be respected or even be taken seriously? No, it doesn't matter who owns the IP, because whoever owns the IP could very well end up ruining it. This goes for Black Isle as well, if Interplay hadn't canned them, if Van Buren hadn't been cancelled and if it had been a relative success then there is nothing that says that Black Isle themselves won't go off the deep end and ruin Fallout.
It doesn't matter who owns the IP. What matters is whether or not their continuation of it respects, adheres and furthers what has already been established. If they don't then they have no artistic integrity and whatever they came up with is nothing more than a bitter joke. Bethesda is already in a bad spot right now as they bought the IP, they didn't create it. And the way they handled the franchise with Fallout 3 was bad, at best. Bethesda walks a thin line, we'll see when Fallout 4 comes out what direction they will go. But if it is as bad as Fallout 3 or worse when it comes to the lore then I'm just about ready to call it FBOS2.
And no one likes FBOS' lore. Even though it was created by Interplay who owned the IP and could do whatever they wanted with it. And even back then no one accepted it as being canon. FBOS went so far against what had already been established that it was not accepted as canon in the slightest. Why should Bethesda be given any different treatment if their lore gets as twisted? Cause its not just Fallout 4 on its own that determines that, it's about what all Bethesda products has contributed to the lore. Fallout 3 had its screw-ups. Whatever screw-ups Fallout 4 has will be added upon FO3's.
The reason why the lore should be respected is because if it is not then what is the point to it in the first place? Why not just turn the series into Saints Row and just have wacky comedy all over the place? If the lore stops being consistent as it is rewritten every game then it means that there is no coherent transition between the games. It doesn't matter what you learn from them. Nothing matters. Why even have any lore at all, why even call it lore? Why limit the games at all? Any and all fictional worlds need to have a backbone that the rest is built upon. The lore is a very important part of the backbone. Take that away and it falls apart.
Or in simpler terms, if Bethesda continues to screw with the lore then eventually Fallout 1, the original Fallout game, won't be considered canon any longer becuase 'it' contradicts the lore.
It's not like it's difficult to come up with new lore. A small company that studied the effects of biological warfare agents on animals survived the blast and the apes or kangaroo's in there managed to escape, mutate through their exposure to the BWA and the airborne FEV. Done. It's not the most well-written but it is new lore and it doesn't screw over any previous lore. Oh and we'd get mutated kangaroo's. If I can do it in 2 minutes then why can't Bethesda do it in 5 years?