We are humans. We need social connection, we need soap operas, "trash TV" is just human drama basically. Our brains were not made for studying math 24/7 but they were made for social interaction 24/7. Social interaction is like driving on autopilot. It fulfills us. Doing science, solving hard abstract problems, being engaged in political events is tiring. Sometimes we just want to do what our brain is made for as its default, resting activity.
Why is it trash also? I'm sure there's a lot of interesting psychology to unpack there. It's just trash if one thinks we need to dedicate ourselves to "higher purposes" and anything else is "lowly" and "denigrating". As if whatever one chooses to do in their free time, that doesn't hurt anybody, and is just a little human drama in a watchable package that maybe we miss during day to day, as so much of a job life is dry, and that makes us connect to our inner humanity is "trash".