That’s the neat part of the Permanent Residency (Green) card: you don’t have to stay forever. What that change does is destroy outsourcing and H1B visa mills by forcing employers to hire domestically first, and actually go through the process of sponsoring an immigrant’s Green Card if they want to hire cheaper foreign labor.
It does not deter expats, it protects them from exploitation and abuse by employers.
Sure, and a hunting license doesn't require you to shoot anything but it would be weird to oblige you to get one if you don't have an intention of hunting?
If green cards are easier to get, then the people that want them, and who you seem interested in protecting from abuse and exploitation can choose to apply for them -- great! It would have this effect even if you don't require every employee to have a permanent residence rights.
If you create the requirement where only someone with permanent resident status can be hired, but you don't make green cards actually easier to get, then you've just put in some protectionist/nativist barrier.
But if someone doesn't necessarily want to be a permanent resident, but does meet some other work visa, and an employer wants to hire them, you're just creating an extra bureaucratic obstacle for them, and claiming that it's for their benefit.
The entire point of a work visa is enforced precarity for the benefit of the employer at the expense of the worker. I do not know how to make that concept any clearer.
If an employer wants someone to work in Country A, then they should be hiring domestically first; if they cannot find someone in Country A and want to hire someone from Country B, then that job is necessary enough that a Permanent Residency permit should be a non-issue for the employer and employee alike.
It really is that simple. If a job cannot be done on domestic wages then it’s not a job that needs doing in the first place.