The NEC allows the use of hardwired rubber cord for some installations but is pretty tight about it.

Here is my guess why, here in the US flexible cords are made of rubber which tends to dry rot.

When I have worked with flexible cords from other countries I find them to often be of better quality, not made primarily of rubber etc.

I would be all for a move away from the US type rubber cords to European type flexible cords.

Bob Badger
Construction & Maintenance Electrician
Massachusetts