The subset of people that could fix the issue that caused the outage was probably .1% of the engineers at FB.
Was FB looking for an excuse to end those rules?
Anything that is simply a current policy at a company basically has to be ignored. It's a nice to have but if you "can't live without that", go look for another job or adjust otherwise.
And even stuff that _is_ in your contract is not a full on guarantee either as contracts can be amended. Which you still have to sign but they will make it very hard for you not to sign those amendments. But at least it gives you some warning when that happens. I.e. you can refuse to sign and then you have time to look for another job while they figure out how to get you fired.
Technically you're correct. If only a handful of employees migrated, they could probably be let go pretty easily. No skin off Facebook's back.
Now if hundreds or thousands of employees migrated, Facebook needs to make a decision whether enforcing the RTO or not will hurt them more. Regardless of technicalities, demanding a non-significant percentage of your workforce to uproot their lives is not an easy ask (or great look).
The article may be misleading, but if employees who were told they could WFH forever now are told to come back that is a change of policy that WILL affect employees. I don't care if you are saying that no one should have moved, there will be people that left. Hell, I work for a much smaller company that didn't state WFH forever (WFH until we tell you to come back, no idea when that will be) and we have had hundreds of people relocate that have stated they will deal with that problem when they ask us to come back.
Of course you can still move away (or do whatever else depending on what other type of policy we're talking about) but you have to be prepared to deal with the consequences.
E.g. if you work for FAANG and you base your life off of a FAANG type salary but now you move to a flyover state, the option of saying "well if you want me in the office, I quite!" is suddenly way less attractive. Unless you were prepared for that. Personally I wouldn't be but I also don't want to work for FAANG in the first place.
You have a relatively low base salary but they wave a bonus of 30% in front of you? Great! Just don't go buy a house with that bonus money (or be ready to deal with the consequences). Some of my dad's colleagues did that in the 80s. They lost their houses when the bonus was reduced/not paid any longer.
Many of us believe there are expectations of companies, contracts whether written or social that should be followed. Even if Facebook reverts their position on this to "back in office" we have the right to complain and/or leave the company (while lamenting that this significantly affects people's lives).
I'm just saying that you shouldn't have too many expectations of companies. If they really meant it, they'd put it in writing. Employment contracts in many many places are written to favour the employer in all aspects.
Another example we could use are the notice periods. You will be hard pressed to find a North American company where the notice period in the contract is longer than 2 weeks, if even mentioned explicitly at all. Never mind states that have no minimums by law. Yet there seems to be a weird "social contract" that expects employees to give a longer notice period in many cases. If you want me to give you ample notice, give me a contract that requires the same of you.