Born in the USA (1984) was his best selling album with 15 million copies sold in the USA. Besides Thriller and Purple Rain it was another blockbuster album of the early to mid 80s. Springsteen was the all-American guy who America just loved. How many copies do you think Springsteen's next album sold in 1987? 3 million. Then until 2002 he never released any album that sold more than 1 million in the US. In 2002 he released an album which sold 2 million. Since then he had one more album that sold 1 million and nothing else he released went even platinum.
I think that comparison works in some ways but not in others. They are very different artists who were at very different points in their career at that time. Springsteen had released 6 albums and built a strong fanbase for 11 years prior to Born in the USA. He had already had his break-out record with Born to Run in 1975. Michael of course had been making music for even longer than that, but was still very much establishing himself as a solo artist when Thriller came out - it was only his second solo release as an adult after all. He was still developing himself as a songwriter, as a producer, refining his vocals, etc. For Springsteen, the Born in the USA album was more or less the culmination of 11 years of hard work. It was a very deliberate attempt to 'go casual' and see what would happen. Michael on the other hand saw Thriller, in many ways, as just the start of things.
This might have influenced their ideas about their follow-up albums. Where Michael reached for even bigger heights, Springsteen purposely decided to scale things back for his next release (the Tunnel of Love album). Instead of churning out another album of poppy rock songs, he wrote an album focused entirely on adult relationships with songs drenched in synth textures rather than guitar riffs. It was bound to alienate many of the casual fans that jumped on the bandwagon in 1984 and that was deliberate. He did not try to repeat the success of Born in the USA. In part, and this speaks to your point, because he knew that was impossible to do anyway. It's also because he simply did not care about (consistent) mainstream success as much as Michael did - they have totally different artistic backgrounds.
However, despite their completely opposite aims in terms of sales for their follow up record, neither decided to follow up their biggest seller with an album that would appease their 'core audience'. Springsteen did not go back to the music he was making prior to Born in the USA (and actually he had already gone through very different phases as an artist until then), but did something he never did before. Likewise, Michael did not go back to making another Off The Wall. And although he may have retained some elements of the Thriller formula for Bad, he kept evolving as an artist (and obviously continued this process with Dangerous and HIStory).
In my opinion it is very difficult to compare artists because every artist, and the situation they were in when they had massive mainstream success, is different. But I guess it just goes to show that they all pave their own way and that many of them want to evolve rather than keep doing the same thing they started out with. James Brown went from being The Godfather of Soul and making primarily r&b/soul music to the Minister of New New Super Heavy Funk. Elvis' second career phase (60s and 70s) was entirely different from the 50s Rock & Roll that shot him to superstardom. Bob Dylan's current music sounds nothing like the music that made him famous. Etc etc.
the formula of his music did not change (he's the kind of artist who always does basically the same kind of music)
Oh, I really disagree with this. This is imo a misconception many people have based on the Born in the USA hits you hear on the radio. His output might have been somewhat stagnant in the last 15 years but he has done a lot of different things in his career. Started out doing very r&b, even jazz-influenced songs on his first two/three albums, then combined it with a Phil Spector wall-of-sound type approach, then went for a sparser, more rural, sound in the late 70s. Did very folky acoustic albums, the adult contemporary stuff I mentioned above. Anyway, that's an entirely different topic!
