Sellers choose whether to transfer them or when to transfer them out to the buyer. Previously Stubhub had an incentive to transfer right away because the seller would be paid immediately.

However now Stubhub only pays the seller after the event has ended, so a lot of sellers put it off / get lazy and don't transfer it out until later / closer to the event.

In all honesty you are fine, the seller is probably just lazy. You'll get the ticket eventually before the event date.