The Beatles were my favorite band in the world for about a year, when I had one of those extended-length compilation albums, and back when I was working through R.E.M. albums every six months or so. It's not hard to see why they'd be the favorite band of someone who was young, since they embrace traditional songcraft, and their more experimental moments are within that framework, so nothing gets too out of hand. It's also not hard to see why a kid might prefer a best-of compilation to the actual albums of other bands. Selecting only the best gives a distorted sense of what a band was about.
That period ended definitively once I discovered The Who's Tommy. I have had limited interest in them since then, though I will confess some enduring weakness for "Rain," "Martha My Dear," "Strawberry Fields Forever," and a few others. The Beatles' problem is that for any particular thing they did in their career, their is another band that did the same thing, at a similar or higher level of quality, for a longer time.
The usual defense for this is "The Beatles did it first, though," which, aside from the various ways in which that's not especially true--since they were building at first on the Brill Building, Tin Pan Alley, girl groups, r&b, blues, etc*--is not much of a defense. If you were alive at the time, "first" holds some importance, but if you weren't, it's hard to see the value of "first" as opposed to "best." After all, Thespis was first, but he won't get many votes for best actor of all time.
I find this phenomenon interesting because it's one common manifestation of a tendency that shows up elsewhere. People sometimes appear to have thought over an issue once in their teenage years, and never quite revisited it since: religion, politics, books, movies and music. I've never quite understood it. During grad school I would occasionally check my work by engaging in the following thought experiment: what would be the case if I were completely wrong on this topic? What are the things I'd be missing, and how would I assemble that argument? It clips one's wings a touch and keeps one honest. My tendency to occasionally revisit things I believe myself not to like comes from the same place: assuming I think the same as I used to is dubious at best, and maybe this movie/author/music will sound different to me now. I have reduced the amount I read on the internet because I get a sinking feeling whenever I find something I agree with too much--am I agreeing because of the strength of the argument or because it's flattering my beliefs? And so also here: the Beatles are a perfectly good band to have as one's favorite at the age of 12, but if they're still the favorite at 30, something has probably gone wrong.
*And if you're concerned about racism, sexism, intersectionality, etc, there's something problematic about assuming that it hadn't been "done" until it was done by white men; this is also the problem with discussions of Elvis' novelty. The better defense of Elvis, of course, is that he was a good musician and entertainer who had one of the really excellent backing bands ever.