No one hates an Oblivion-with-guns, people
only had problem with it when Oblivion-with-guns had the Fallout name pasted on it. They could've made their own IP - the Fallout brand before Fallout 3 was useless in marketing anyways because anyone in the target audience of Oblivion-with-guns would probably never have heard of the name. That's the problem - why remake a series into a completely different genre (as with EA's Syndicate) when the original fans won't like the new one, and the old fans will never have heard of the old one? It's pointless as a marketing-by-brand strategy, and it only seeks to reduce your potential customer base.
What say some other world where Van Buren got released as Fallout 3, then the Fallout series died
, while Bethesda made their own Oblivion-with-guns IP and it got big?
Meanwhile, somewhere in 2014, Obsidian on Kickstarter manages to fund a new, proper Fallout 4 and it gets released? That would've been - and currently is, with other devs - the outcome with several other old IPs long forgotten.
Well, yes, the wrist-mounted inventory, the SPECIAL system and the VATS aiming system were the only unique factors in Fallout 3, and the main selling points, but
none of those were exclusive to Fallout. The SPECIAL is an RPG ruleset that could be used for any RPG really, the VATS was a new mechanic entirely that never had to be named VATS, and the wrist-mounted inventory didn't have to be a Pip-Boy.
Bethesda had no obligation nor marketing-related reasons to slap the Fallout name on it, so it's possible they may have been either shortsighted or too lazy to think up a new title for a shooter IP.