The 1970s seem to have seen a lot of songs and albums making meta-commentary about music and the rock lifestyle, such as Don McLean's 'American Pie', The Eagles' 'Hotel California', or Pink Floyd's 'Wish You Were Here'. Was there something about the '70s that made this so?

Adapted from a previous answer:

I don't know that it's true that meta-commentary about music and the rock lifestyle was more prevalent on the 1970s than any other decade during the late 20th century. The theme of the struggling rock star, for example, is a natural one for a rock star to discuss, because, well, aspiring rock stars soon discover, if they're lucky enough, that being a rock star is great in some ways, but not necessarily good for your mental health. Firstly, the peripatetic lifestyle rock stars typically lead means that they spend much time away from support networks, which is likely to exacerbate pre-existing mental health problems. Secondly, the mythology of the rock'n'roll lifestyle is not one that encourages moderation, shall we say - access to poor lifestyle choices is easier than it would be for some regular schmuck, and fans and PR people kind of expect you to live the lifestyle. Thirdly, the nature of the power imbalance between you and others - you being the big rock star - means that there's little punishment for simply removing from your life people who tell you things you don't want to hear, and thus you end up surrounded by 'yes men' (as Freddie Mercury does - in fictionalised form, at least - in Bohemian Rhapsody), which becomes something of a lonely existence because very few people are on your level. Etc.

As a result, plenty of musicians have made comment in their songs about the rock'n'roll lifestyle between 1964 and 1999. Ones from before the 1970s:

1965's 'So You Want To Be A Rock'n'Roll Star' by the Byrds
1968's 'Street Fighting Man' by the Rolling Stones
1968's 'The Story of Rock and Roll' by the Turtles
1969's 'The Ballad Of John & Yoko' by the Beatles

And after:

1980's 'Super Trouper' by ABBA
1982's 'We Are The Road Crew' by Motorhead
1986's 'Wasted Years' by Iron Maiden
1987's 'Wanted Dead Or Alive' by Bon Jovi
1990's 'Freedom '90' by George Michael
1994's The Downward Spiral by Nine Inch Nails
1996's Pinkerton by Weezer
1997's 'Look Inside America' by Blur
1998's Mechanical Animals album by Marilyn Manson
1999's Machina/The Machines Of God album by the Smashing Pumpkins

And that's a quick list that misses out plenty of things.

But what changed in the 1970s compared to the 1960s was that the rock'n'roll ecosystem changed; it's in the 1970s that the rock'n'roll touring lifestyle really gains steam, as the technological and social problems of playing in large halls and arenas effectively get solved; as a result, you get increasing numbers of bands playing these circuits, and increasing amounts of people going to big rock concerts. The 1970s was also an era where rock'n'roll had reached a kind of critical mass, enough so that it had splintered into sub-genres - glam rock, hard rock, heavy metal, punk, country rock, etc. Of all the eras of rock'n'roll, the 1970s might be the era when it had the most critical mass in this sense, when it was the most inescapable (the 1980s saw the primacy of the classic rock doctrine challenged by MTV's focus on surface-level glitz, and by the 1990s, rock was also challenged by hip-hop and dance styles).

Additionally, by the 1970s, the 'hippie aesthetic,' which aimed for a certain kind of (male-dominated) authenticity, was in full swing (where it had developed over the second half of the 1960s). By the hippie aesthetic, I mean a certain set of assumptions (identified by John Covach) common in late 1960s rock and flowering in the 1970s: a belief in individuality and personal freedom, a Romantic view of the nature of art, a fetishisation of the electric guitar, a certain anti-establishment attitude, a recognition of the importance of writing your own songs, etc. As a result, because these people were focused on individuality and authenticity in that way, it's natural for them to write about their own individual experiences (or at least look like they're doing this) and expect that to be seen as a mark of authenticity. John Lennon and Paul McCartney in 1963 were writing 'From Me To You' - a song very deliberately written to appeal to their fans, where they didn't have strong feelings about the sentiment of the song . But by 1965, John Lennon had come to believe (particularly through listening to a bunch of Bob Dylan's early 1960s folk songwriting) that he needed to write songs that explored his actual experiences, with a certain aim of authenticity - so something like 'Help!' is a (somewhat disguised) meta-commentary about the rock lifestyle, and by the point of the Rubber Soul and Revolver albums, Lennon was writing songs that were fairly obviously about his own life as a rockstar - 'Norwegian Wood' comes to mind (being about having a one-night stand, and having a very John Lennon perspective/sense of humour), as does 'Nowhere Man', where Lennon berates himself for his frustration and inertia living in his big mansion when he's not on tour.

As a result, you start to get things like 'Wish You Were Here', which was very well known to be about the band's previous guitar player Syd Barrett, or 'Long Way To The Top' by AC/DC (more specifically about the rock lifestyle and how hard it is), or 'Hotel California', a more oblique, metaphorical view of the whole enterprise. Meta-commentary on rock history like 'American Pie' is a somewhat different case - not so much being about the rock lifestyle - but the development of the hippie aesthetic (or what some in music criticism called 'rockism') made 'American Pie' possible, because it implied a certain cultural view of what is important and less important in the music, and thus which bits of its history to highlight.

Anyway, in the 1970s, the rise of the rock'n'roll tour, and the rise of the hippie aesthetic, mean that the rock'n'roll lifestyle became a topic of lyrical discussion. But it seems to me that, in music which evolved from the rock of the 1970s - whether that be the hair metal of the 1980s, or the grunge and alternative of the 1990s, varying versions of the 'hippie aesthetic' were retained, and so plenty of those groups did the 'grumbling about being a rock star' thing through the 1980s and 1990s, to the point where it had sort of become a cliche at a certain point in a band's career when they'd run out of other lyrical content to discuss because their lives basically now revolved around touring.