When an account is inactive for 3 years, it automatically receives the old suffix and is available for new accounts to take the name.

Also, just delete old accounts that's last activity is also their join date, they're just taking server space.

As seen lately, people from like 2007 are still coming back, deleting their accounts is just harsh

We do not delete accounts. Consider posts, items and transaction histories. All these things would become very messy if we deleted accounts.

We could perhaps rename accounts that have never even been logged into, but even if we did, nothing would really improve. Hence we are in no hurry to do it.