From albums about bands' struggles in success (like The Rise and Fall of Ziggy Stardust and the Spiders From Mars or Rumors) to individual songs (like It's A Long Way to the Top If You Wanna Rock And Roll or Rock and Roll Band) to even rock operas (like The Wall or Tommy), there is no shortage of prominent 1970s Classic Rock that deals with this theme. Other decades don't seem so obsessed with it. Why is that?
I don't know that it's true that the 'struggling rock star' trope was more focused on the 1970s than any other decade during the late 20th century. Firstly, of your examples, Tommy was released in May 1969 (though it was most successful in the charts in mid 1970), and The Wall was released in November 1979, and didn't hit the top 10 of the U.S. album charts until 1980 - so, you justify only one of those as 1970s, depending on what criteria you pick.
Secondly, the theme of the struggling rock star 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:
And after:
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 1960s). The hippie aesthetic encouraged many musicians to write about their lives and preoccupations, as that would be more honest; contrast this with, say, 1962's 'From Me To You' by the Beatles, which was deliberately written as a love letter to fans by a group that had not (at this point) considered self-expression a valid lyrical concern in comparison to giving the fans what they wanted.
Anyway, in the 1970s, the rise of the rock'n'roll tour, and the rise of the hippie aesthetic, mean that the demands of 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.