I am familiar with the development of musical styles, where the styles usually start out in smaller ensembles, with limited notation, relying heavily on improvisation, then growing in size adding more notation, with fewer and fewer improvisational opportunities. You can see it happen in all kinds of styles from Argentine tango to blues even western swing. What kind of puzzles me is that rock and roll, never really developed past the small ensemble. After a little searching, the only large bands I could find were Chicago and Blood Sweat and Tears. I wonder why this is? I was thinking it might have to do with the guitar technology, but then there are plenty of big band blues and funk groups.
R&R has likely stayed in small groups because it's a style that could be played by a small group of people, or even just one person.
It's not, or, doesn't have to be "technical", or polished, or even "good" for people to enjoy.
People can just "plug in and go", or strap on an acoustic guitar and play away.
Unless it's a long piece that's orchestrated (Tommy, Green Day's American Idiot that's now on Broadway, etc...) rock music just doesn't need more than a couple people (unless someone wanted to have a large group) to be performed.
There were several larger groups in the 70's that were popular. Ohio Players, Sly & the Family Stone, Santana, E,W & F, ELO, just to name a couple.
Why larger groups haven't been popular in a while, who knows? A lot of "performers" have large bands behind then these days though.
I've played in 6 piece rock bands, and we played "the songs", and didn't improvise because of the different instruments involved. The parts were written, and songs orchestrated, so that's what we did.
I've also payed in cover bands that had several players, and we could stretch a little in certain things.
My blues rock trio does improvise, and it's easy, because only one person is playing each instrument, and it doesn't get cluttered and confusing to the listener.
Having competent players is also important in this area too
I've always felt that nothing really has to be shoved down peoples throat, they just don't have to buy the music, or listen to it if they don't like it. There
are lots of "mouth breathers" (haha) out there, but people can just turn the channel, or, turn it off.
There's the real power.