This is funny, but I always got the implication from the books that there had been people trying out for Seeker, but none of them had been very good. So McGonagall stepped in because she loves her House team.
Harry Potter is the default fandom. Everyone is born into it. We join other fandoms, but even if we say we aren't in the HP fandom, we really are.<<--it's been some time since I've read the books but this is relatable
21 Reasons "Harry Potter" Has The Most Dedicated Fandom Ever