I think it's partly biological insofar as people tend to be less adventurous in life in general after their 20s at the latest. by then you in theory are settled into life routines that will carry through most of your life, be it food, media, political, any other habit or taste. this isn't a hard or fast rule but I think it's the general norm if someone doesn't actively search out new stuff
I felt myself starting to slip into this the past couple years where I wasn't really discovering much new music, this year I've committed to listening to a new album a day and it's really broadened my horizons. ironically I've started with older stuff, like the stones, the who, dylan, elvis, kinks, byrds, etc. where I'd mostly not actually listened to full albums or their broader discography, and have been working my way forward it's been quite fun.