I may be wrong, but I think at least back in 80’s you could always use a tee to kick after a safety. The reason for the punt was that there was no chance of a touchback off a tee and the hang time of the punt made it worth punting. Since the kicking team can’t get a running start anymore, it would make sense to use a tee and just kick it as far as possible. Hang time is irrelevant now. But I could be mistaken. Perhaps the rule was changed at some point that tee’s weren’t an option on safeties.