I think the problem could be worse. Fortunately for Fallout, their games are pretty big and popular, and the tv series is bringing people back to their games. And they seem ready for it as Fallout 4 is getting a quality upgrade, reportedly. While I agree the timing of release for the show would have been greater with a new game to the series coming out as well, I think the way they're doing it lets the new audience get into the previous games to catch up on things. It sounds like the show is quite good (watching tonight) so hopefully they'll have a few more seasons. And maybe they can end it with Fallout 5 releasing.
Anyway if any of the tv shows have a bit of a problem, may I remind that the Twisted Metal series came out at a time when there's 0 of the namesake's games on PS5, and all the console got was Destruction Allstars instead. In fact at least one report says a Twisted Metal game in development was cancelled due to layoffs. So that show's really missing its marketing potential as well.