What’s with this epidemic of anime high schoolers living alone
It’s a very common trope. Sometimes it serves to indicate something significant about the character (they’re exceptionally lonely, or neglected, or they’ve had to act grown-up prematurely, etc.), but sometimes it’s just a “clear the decks” plot device that avoids including extraneous characters and allows the character to go places and do things without reference to parental control (and in romance series allows couples to be alone together).
There are plenty of series where the characters may not literally live alone, but the parents are never seen even if they supposedly exist.