One beautiful thing about loops is that they allow smaller teams to create games. The loop is content and takes real, hard work. When you play a "do everything" game like Breath of the Wild or one of the modern Final Fantasy games the amount of content is staggering and completely unapproachable by most small teams.

Another beautiful thing about loops is that they enable short sessions. I love games like this. You can sit there for a few minutes, enjoy your time, then move on to other things. Wordle is like this. I love games that are content to be played occasionally.

I like your example of Bolero. This is a good formula for longer games: iterate on the loop and have it slowly transform and crescendo as the game moves on. I would argue one mistake some games make is that they want a lengthy game but they don't do the Bolero thing; the experiences late in the game are not meaningfully different from the experiences earlier in the game. Even games without stories have an arc, and if you don't manage that arc then yeah I can see why people would end up getting bored.