That sad thing is that even the success Fallout 4 is still wasted potential, and that's because it's not an MMO.
Fallout 4 has optimal design for a multiplayer game - longevity through repetition, so there's never a shortage of content, but all it does to singleplayer games is make them more boring. Quantity over quality is fine when we're talking about something you can come back to do again and again with friends, but as it has been stated before,
anything is fun with friends. Bad movies and drinking nights are good examples

.
It's an offline MMO in all senses - the fun with MMOs comes from the social aspect, and take a look at why Fallout 4 is popular. People keep sharing their created characters, their settlements, and screenshots with everyone else on social networks. Fun little finds like skeletons and graffiti messages? Yes, common in MMOs too. There's nothing in Fallout 4 that hasn't already been in an MMO.
Say, you know what? Tweak the lore a little, tear the Fallout name off, and add multiplayer - instantly beats Destiny and The Division with its charm, customisation aspect and unique setting keeps it lively, plus a multiplayer game with modded servers? That game would be a win. Not my kind of game, but I know that it would be fantastic for a lot of people out there (especially the ones who profit from it

).
Bethesda Game Studios lost more fans than they should have when they decided a fairly unique, slightly unpolished, sparkly little open-world MMOFPS should be a Fallout game. They lost the respect of the Fallout 3 fans, and from what I've seen, even the Skyrim fans.
But, I don't think it's because tried to make an MMO and decided to slap the Fallout name on it so they could roll two projects into one. No, I think it's because they legitimately thought it would be cool to take from the all the games that everyone likes nowadays, not noticing that every game they took their inspiration from had multiplayer for a reason. I feel like they're unaware of what they've created, and just thought they accidentally stumbled on the next big thing, Minecraft-style (ironic, isn't it?).
It just so happened that it was also a perfect game to market for maximum profit, and Bethesda Softworks milked that opportunity for that they could. Now, I have nothing personal against casual gamers, or businesses, but my final opinion is that Fallout 4 has been a demonstrative case of unaware casual game developers being led by money-first businesspeople. This is what I believe happens. This is what has happened. This is what will happen again.