Why does Casdoor generate a new access token on every login instead of reusing?

Hello, I am using casdoor for authentication to our service. We noticed that casdoor generates a new access token on every login. Why is this the behaviour. Ideally it should reuse the old access token until its expired. Is there a reason for this implementation?

each login is a standalone session, and with a new access token. each login's time is different. I don't see why re-using token works. because your 2nd login session time range is shorter