This is actually a much harder sell than a 6 person party. D&D is based around 4 basic roles and has been for quite a while and lacking one of those roles can be problematic. 5e makes it possible to approach the basic roles in a couple of different ways, but it's harder to hit all of them in just 3 party members. I'd be fine with a party that size on tabletop, but it would make designing challenges for a CRPG a bit too erratic as it would be harder to predict what abilities a party wouldn't have. Also it would cut off access to storylines and thus XP.
There's very little in favor of reducing the party minimum.
