When we migrated DNS to route53 in early 2019 we discussed moving registration as well. That conversation took about two minutes and ended in a hard no.
Our registrar is MarkMonitor who specializes in large portfolios.
I’ve got a dedicated account rep. We know each other well. We talk often, not just domains but college sports, etc.
I need something I email my guy and it gets done.
Registering a .es domain requires a scan of my drivers license. He handles that.
Transferring in .am domains during a recent merger required an authorization letter, on letterhead, signed by a corporate officer.
We don’t have any .at but I’d put 20 quatloos on there being some sort of requirement that AWS can’t just drop into a web interface, combined with the fact you don’t really have phone support until you qualify for Enterprise Support.
My primary role is near what you’d call Cloud Architect, domains and DNS are a side gig that ended up in my lap. Being disappointed in how AWS does something is sort of a theme in my life.
In this particular case however I’d bet the issue is with the AT registry wanting something.