Edit: I thought you linked to yet another famous band. People keep doing that... 99% of bands a normal person would see in normal life don't even have a wikipedia page.
However your link looks about jazz.
A common rock band is rarely good with more than 4 members because people lose unity and it's just technically harder and people are rarely professionally trained.
Honestly I wouldn't know anything about rock bands because I don't listen to it at all so you could be very right. I just responded because this thread was talking about string/barbershop quartets, which are almost definitely 4 parts because that is the minimum number of people required to make a 7th chord, and then again because you didn't know what a Big Band was, which I suppose is very understandable, but as somebody that grew up around and playing on them it's super foreign to me.
However your link looks about jazz.
A common rock band is rarely good with more than 4 members because people lose unity and it's just technically harder and people are rarely professionally trained.