While tabletop games recommend a party of 3-5, that's partially to do with social gathering limitations, partially to do with shared interraction time of human players, and partially to do with strain on the DM to keep a cogent and engaging story running for everyone and keeping them all feeling equallly involved.
None of these are major considerations in a video game format; the shift to a video game format removes every one of them as a problem or limiting factor. Conversely, in a video game format, even one that supports multi-player options, the main consideration is the game as played by a single person.
So, then, we can look at the history of D&D video games: Unsurprisingly, *most* of the D&D video games that involve a full party have their party limit set between 5-8. If nearly every D&D video game does this, consider that there are legitimate reasons why.
Bingo.
It's also (one of) the reason(s) why in a tabletop session usually you deal with whatever amount of players you can get and whichever class and (if it's a factor) alignment they happen to be and try to "make it work somehow", while on most CRPGs the player is typically offered a vast cast of optional characters that far exceed the number of party slots available and that in most cases keep "orbiting" around the player even when not directly part of the active group.
