If you have a profitable franchise that you don't give a shit about and have basically just hijacked off of the original owners, making shitty games that you know will sell well doesn't seem like too much of a bad idea.
I honestly try to avoid conversation about Fallout with my friends, for this very reason. It's hard to get in to conversations about Fallout IRL for me, because people talk about "Fallout" as though a newer part of the series is overall representative, and then don't quite understand when I try to correct them.