It's probably what you've said. I think perception changes, all the different venues and different types of music were once exciting. Then your brain forms the patterns and isn't as excited by x,y and maybe only z elicits a reaction.

Then you become more and more a morning person, so in the evening you aren't even that hyped up and your brain is already trying to call it a night.

For me something like standard 4x4 techno has become so formulaic that it doesnt interest me as much