The IMDb Top 250 for Television is an absolute joke.
Going through the list all I see are shows that are only there because they're popular, were good at one point but overstayed their welcome, hit and miss per season, or shouldn't be there at all.
Take a look at True Detective at #21. It's two seasons in and even hardcore fans hate the second one. I don't think that something that has been 50% good deserves a 9/10. Deadwood is at #81 which is fine except that the show didn't even have an ending. A Clockwork Orange is #81 on the movie top 250 but do you think it would have the same score if it just abruptly ended and we had no idea what happened to Alex 655321?
Here are a few others: This is Us #54, Parks and Recreation #129, The Walking Dead #203 Person of Interest #249, Entourage #194, The Muppet Show #198
A lot of the shows are in its first season and have amazing scores and if the future seasons are mediocre, users won't go back to re-vote.