Sitting in class sophomore year on the California north coast. Probably bought the record the next time I was able to get over the hill to a record store, $1.98 plus tax at KFD Department Store, since it was, of course, the new Beach Boys album, and was blown away at first hearing. Still am. Absolutely loved it, and never once had a thought about what seemed to confuse or even repel so many fans (and evidently Capitol Records) at the time.
I could see it confusing people and the label a bit if they went straight from All Summer Long to Pet Sounds. That would've been a bit jarring.
But, they had, three studio albums that I thought bridged the gap.
The Christmas Album - Their first real departure from surf / car songs. Granted you had Little Saint Nick. But songs like Christmas Day and the orchestral arrangements of the Xmas favorites show a more mature direction for the group.
Today - No car or surf songs again. More complex songs like When I Grow Up, Kiss Me Baby, and Please Let Me Wonder.
Summer Days Summer Nights - There were a couple songs like California Girls and Amusement Parks USA that were more akin to the BB early themes, but the arrangements are much more sophisticated, especially the intro to CG. Let Him Run Wild and (non album track) The Little Girl I Once Knew wouldn't have sounded out of place on Pet Sounds.
Maybe Party was the monkey wrench that confused people........