Why is Buffy not seen as a teen drama ?

I mean, when people talk about the greatest teen drama of all time, you will automatically see classics such as One Tree Hill, The O.C., Gossip Girl and so on. Sometimes, Buffy is on their list (and when it is, it's often at the very top) but people will often put in parentheses "if we can consider it a teen drama" or stuff like it, despite the show being apparently (according to this fandom) most well-known for the high school year.