I have no idea what an average user with trusted infra would benefit from having never met one.

You rightly point to the burden of managing a cert environment but as smallstep and Teleport have demonstrated that more streamline experiences are available in the open source arena.

Having made the switch, and with the right "trusted infrastructure" it's not too much of a burden and where you have a non-trvial number of people to look after, definitely worth it was part of a wider Zero Trust ecosystem.