In larger companies this is rarely your decision to make and in three different issue tracker migrations I've seen the team responsible for maintaining the issue tracker instead to keep the old tracker in a read only state until they either have to renew the vendor contract or make security updates, at which point the issues go down the drain. This may all have happened before you joined, so it's not likely you could have done the migration yourself (and the security team may have disabled generating API keys which automated migration tools need, anyway)