The reason why Sgt. Pepper is there is simply because it was released at the beginning of the summer in 1967 - not planned to be a heralded beginning to the "Summer Of Love" which was called that by the press well after the fact and out of convenience, but rather another case of a group like the Beatles having better timing in history than some of their peers. Again, through no grand scheme or plan, but it just worked out that way.
Take a look at summer 1967, and whether or not we agree about it the Pepper album was a constant presence and influence, and easily the most-talked-about release that summer and into the rest of that year. Something like that gets burned into the collective memory as being associated with "the summer" if it was coming out of radios and record players everywhere you turned in summer '67. And even with the lack of a "hit single", AM top 40 stations had the album cuts from Pepper in steady rotation, which was slightly unusual for that singles format.
More to do with timing and history than a perceived pro-Beatles bias, IMO.
Very, very true and I think I agree with your view that it was it's release that made it a "summer" album. But quite frankly, that's the worst reason to label it a summer album. It's like releasing an album called "Winter Hits, OR How I Like To Stay Cold" during 86 degree weather.
Worst reason? Not by a long shot: See the Wild Honey justification for that
! You might be missing the point: If the Pepper album became the soundtrack of the summer of 1967, and that summer passed through history as the grand exalted "The Summer Of Love", and people told the stories of how Sgt. Pepper was heard everywhere that summer, it gets the instant connection to that summer and the impression that the album was one of the soundtracks to the so-called "Summer Of Love" became a powerful association which will always connect that album to summers in general.
It makes a lot more sense than Rolling Stone's grasping-at-straws approach to maintaining some hipster-underground cred by listing Wild Honey so high, an album that has *no connection* to anything resembling summer apart from maybe the bee on Marilyn's stained glass window, was released in late '67 just as fall 1967 was breaking into winter 1967, and above all the album's title and title song were less about the jar of honey and more about a girl ('honey') who was wild, and the guy who was wild for her.
I love Wild Honey, it's a great listen anytime, but talk about the worst reason...it has nothing to do with summer at all, especially in light of the other BB's albums that *do* celebrate the summer quite openly and honestly.
In Rolling Stone's defense maybe they're drinking too much Pabst.