Why do some hashtags have top posts from months, even years ago

Why does that happen when there are many new posts with these hashtags?
for example: #memeposts (5 top posts are from 2019, and others are a couple months old)

Engagement with the posts probably

IG has an algorithm, it could watch more than time of posting: account size, engagement for that post, engagement for the account. It's still hard to tell, but you can play around that hashtags (try #bestmemeposts or something like that ) to get close to the initial one.