But for some American born engineer who has family outside of SF/NY/LA, being able to work remote while staying near family/hometown would be awesome for himself, the hometown and ultimately residents of those mega cities too as they would see some relief in ever increasing cost of living.

Google/Facebook/etc have to pay a lot higher salary to keep talented engineers in/near SF because of much higher cost of living.

Those employers probably COULD save $ if they paid lower salary and allowed full remote working. Even if they flew in the engineers on chartered jet every other week and housed them in hotel for regular face-2-face time in HQ, they still probably would end up saving $ in the end. Like instead of paying salary of half a million a year, they could pay $300,000 and use the $200,000 for chartered jets and housing when they are visiting SF.