Why? Dragon Age, Knights of the Old Republic, Mass Effect all had 3-4 party size.
You say that as if that made them any favor. Which it didn't. Or as if they were the gold standard for party management, which they weren't.
That aside... Entirely different systems, rulesets, type of RPGs, etc. Not to mention that at very least Bioware understood the importance of having an extended cast outside of the active party and let you swap companions in and out across the entire game... Which if we have to believe their original claim Larian is actively planning against, instead.