Personally, I don't think they'll find a way to make EVERYONE happy. Someone isn't going to get the option they want (100% wfh? work at a remote location because they don't like the main office? etc). There's no way they can.
BUT
The group speaking up CAN put more pressure to have options that will make more people happy. If hundreds of employees say "Look at the numbers and look at news stories talking about 40%+ of employees willing to leave a job without WFH and etc"...
If I say "I'm not open to 100% in the office" and Tim says no?
If 80 say it... if 2800 say it...
Tim can ignore 1 person. Can he ignore 80? 200? 2000?
If you aren't interested in leaving but you want better options then you have two things at odds with each other. You may be interested in staying but if staying means you work in a office you hate or have a commute you hate or whatever... then that's on YOU to decide what's more important - a job at apple or a job with WFH.
At the end of the conversation... the letter tells Tim (or whatever CEO gets a similar letter with more than a couple signatures) that he risks losing a sizable number of employees. That letter isn't from one person... it's from a large group of people.
It's up to Tim to decide if the risk of losing talent is worth sticking to the currently given options.
It's up to you and me if it's worth the lack of option you want to stay at the current job.
Like i said... I'd probably look for work if asked to be in the office 5 days a week due to my commute. I don't blame them for asking and given some thought I don't think a letter from a "union" or "employee group" in this circumstance is bad.