There’s also the little matter of just how many different instruments you’re willing to cart around just to match one song in the set to the studio version.
That said, who wants a live performance to be an exact recreation of a studio one you can hear anytime you want anyway? In many cases after years of fine tuning a live performance can blow away the original studio track.
No doubt. There are also artists who just sound better “live” than they are in studio. Joe Bonamassa is a perfect example of one of these artists for me.
You can do a lot with 3 guitars. But then have a look at the instrument rack that someone like ZZ Top tour with (around the 10 minute mark). McCartney tours ridiculous crowds, so there’s no shortage of money to support carrying around a few guitars.