Job offer overseas might be too good to turn down. A regulation like this would then deny this couple a potentially big improvement in their quality of life because there would be no income mobility for them. They would be unable to rent their place to go try out a potentially life changing opportunity in a different country. Regulations like these always end up having unintended consequences and hurting random people like this.

I did, but TBH, I think that makes me (and most of HN) part of the economic class cities want to keep out of their culture, and I don't blame them.

Bought the house, then got a long-term assignment/promotion in another city, but 100% plan on moving back in the future.

This is not uncommon.