Fantasy appeals to a wider audience (see the "Romantasy" genre) and seems to overlap more with YA fiction so captures more young readers.

Yes. What's popular with teens varies over time, of course. At peak Twilight, the Barnes and Noble at Hillsdale Mall had seven bookcases of Teen Paranormal Romance. I mentioned this to one of the store Goths, and she told me that vampires were on the way out and the next thing was probably going to be zombies. The Monster Hunter thing had a brief moment.

Then we had the survival period - Harry Potter overlapped the Hunger Games and Divergent eras, all of which produced too many spinoffs. This moved into the Game of Thrones spinoffs. Now, dragons seem to be out, except that Anne McCaffery is back on the shelves.

The latest shift is driven by "booktok" on TikTok. I just saw teenage girls giggling over the new books in the Romance section, while avoiding the YA section. The Dark Romance subgenre is in, and now has its own shelf space.

Hard SF? Other than the Expanse series, not much recently.