I recently set out on a journey to be more cultured by listening to the top 100 albums of all time.
It struck me that a disproportionate amount of top albums come from the mid 60s to late 70s - about 70 made the list I’m using. In contrast, 28 albums are 80s/90s, and only one from the 50s and one from 2000.
So what gives? What factors led to that time period dominating album sales and cultural impact?
While there are many lists, I used this one as it is an aggregate of several lists and factors: http://www.popvortex.com/music/100-greatest-albums/. But looking at a couple others, the trend seems to be the same.
An edited version of a previous answer:
Broadly speaking, what's special about the albums on those lists of top albums is that they very often played a role in establishing what Covach & Flory's textbook What's That Sound calls the 'hippie aesthetic'. The hippie aesthetic goes for music with hippie values - values of free sexuality and expression, peace and love, music trying to say something rather than just be love songs, music with overtones of drug use, and usually very heavily based around white male singer-guitarists. It also focused on the album as a means of expression (as opposed to singles which were more focused on pop) - and the music that broadly speaking followed the 'hippie aesthetic' came to be called 'rock' (as opposed to the more singles-focused dance-oriented rock & roll of the 1950s).
The music of the hippie aesthetic in the 1960s was more or lesss coded as white male music - for starters, the distorted guitars and thumping drums in the music were taken as indicators of testosterone. There's only a few well-known female singers in the era (Grace Slick, Janis Joplin) whose music has the hippie aesthetic. There's also very few African-American musicians who had the hippie aesthetic - Jimi Hendrix being the obvious exception - because the hippie aesthetic was something of a white ideal; the popular politically-motivated African-American musicians of the period - Curtis Mayfield or Bobby Womack, for example - generally had a more community-minded, inclusive message, and wrote songs about the dangers of drugs and the foolishness of hippies. It's also a very 'baby boomer' kind of music - the 1960s is when the 'classic' baby boomers were young adults (e.g., someone born in 1948 was 18 in 1966) or teenagers (e.g., someone born in 1955 was 13 in 1968).
With all this in mind, the mid-to-late 1960s was when the hippie aesthetic was at its peak commercially, and so the popular hippie aesthetic music tends to be lionised. Additionally, The Beatles, Bob Dylan, The Beach Boys, and the Rolling Stones probably did the most to usher in the hippie aesthetic, and being 'the first' is often important in the way that the hippie aesthetic is discussed; for example, in 'Like A Rolling Stone' Dylan was the first to have a hit with a song that combined rock instrumentation with poetic lyrics and social commentary, and his 1965 album Highway 61 Revisited had an 11 minute long song with rock instrumentation on it ('Desolation Row'). It's impressive that Dylan was doing those things in 1965, say supporters of the hippie aesthetic (though whether he should be doing those things was something that the people shouting 'Judas' at him at his concerts fervently disagreed with, and they perhaps had a point).
And because baby boomers like Jann Wenner went on to found magazines like Rolling Stone and occupy important positions in the music industry relatively quickly, and then kept those positions for decades, the hippie aesthetic was basically unchallenged in the music industry until the late 1970s punk era.
Where in the mid-to-late 1960s, the nature of the hippie aesthetic was still in flux, by 1970 it was pretty set in stone; but because pop music is founded on novelty and fun and upbeat stuff, there were only so many ways to make hippie aesthetic music that was also popular, and they'd largely been done. So big albums of the 1970s like Rumours by Fleetwood Mac or Frampton Comes Alive by Peter Frampton didn't quite fit the aesthetic, and so tend not to get very high on the lists despite their popularity (Rumours was #72 on Rolling Stone's 1987 best albums of all time list, and had got up to #25 on their 2003 list, as the hippie aesthetic faded slightly, even at rolling Stone). African-American music tends not to get on those lists either, for similar reasons - it rarely fits the hippie aesthetic. Though there was a brief-ish period in the early 1970s where African-American music did fit the aesthetic somewhat, so you get Stevie Wonder and Marvin Gaye doing music with ambitious scope and a peace-and-love message, which fits the bill - otherwise black musicians are generally on such lists only if they've influenced important white artists.
So the only way, really, for newer bands to get on such lists is to be at the vanguard of new alternate aesthetics, and probably to be white, male and either a baby boomer or making music aimed at baby boomers.
Punk was a music still made by baby boomers - Johnny Rotten was born in 1956, Johnny Ramone was born in 1948, Joe Strummer was born in 1952 - but it was made by slightly younger baby boomers who'd rejected the 'hippie aesthetic' for an aesthetic which had different values - obviously a more cynical, nihilistic worldview, for starters, and more focus on shorter, sharper, angrier songs. Ultimately, this music was still rooted in the 1960s though, in the garage rock that collected on the 1973 Nuggets compilation, along with the music championed by outspoken critics like Lester Bangs - the Stooges, The Velvet Underground, etc. The punk movement, more generally, is a big reason why the Velvet Underground get on top lists of all time, despite their initial lack of success - the punk movement lionised 1960s garage rock, as it was seen to have a vitality and directness that the hippie aesthetic stuff lacked (while still having a political stance rather than mostly being love songs). So you get the Sex Pistols covering The Stooges' 'No Fun' and The Monkees' most garage rock song, 'I'm Not Your Stepping Stone'.
And therein lies the rub in terms of your question: more or less, the top 100 albums of all time lists are usually the top 100 rock albums of all time, because the people who make them are ultimately rock oriented - for them, it goes without saying that the top albums of all time are rock albums, usually; you'd get a very different list if you asked jazz aficionados or hip-hop fans.