FSF wants to be able to relicense as/if the legal landscape evolves, but in a way consistent with the original license aims. I fully support this (and I want to give them this flexibility), but admit that this is based on my trust in FSF more than anything else.
FSF wants a contribution agreement to ensure that it doesn’t have to litigate with 1000s of companies who might claim some contribution that an employee of theirs made was corporate IP*. I also understand this, particularly given the incentive for a company to intentionally cause a “tainted” contribution to get into FSF products.
My willingness to “go along” with an FSF CLA is much, much greater than for a random company who wants to trade on and benefit from the goodwill of the “we’re open-source!!” banner and yet be able to rug-pull later.
* - I think I have exactly one tiny change into emacs from decades ago. It took me way longer to get corporate sign off on the CLA than it did to author the change.