Why do some conjugations of démeurer use avoir?

Bonjour Vanessa ! "demeurer" is one of these verbs that can take either avoir or être as auxiliary in compound tenses. Here is a link to the related lesson: https://progress.lawlessfrench.com/revision/grammar/demeurer-can-be-used-with-avoir-or-etre-in-le-passe-compose-and-changes-meaning I hope that's helpful! À bientôt !