Maybe I'm misunderstanding, but I don't really see the problem with the US system.
I can opt into a fixed 30 year mortgage, which I can exit at basically any point through a refinance or sale event.
I can't port my terms, but my rate is also fixed for up to 30 years unless I exit the arrangement. That's a safer deal for me than having 5 years of fixed interest and then being completely at the mercy of market rates.
At least for me - I'm fixed at 2.25% on a 20 year mortgage. Which was only possible because I exited a mortgage through a refinance to bring my rate from 4.4% to 2.25%. Right now if I refinanced, my rate would be much higher - so I will defer borrowing lots of money again.
Basically - The US system only feels weird when we experience particularly strong movement in interest rates. If the rate stabilizes at 7%, no one is going to bat an eye at getting a loan at 7%. It's only during this window where 18 months ago I could get 2.25% and now it's 7% that feels off. And even now - it's not off, there are just lots of folks in a position where their current mortgage is now a steal, and selling sucks since they lose the benefits.