Alphabet felt more like just a genuine restructuring/clarification that Google is just one of Alphabet's many products. They had no immediate threat in sight at the time?

Meta case could be seen as leadership trying to seem innovative to make up for their core products possibly being in trouble, because they have the immediate threats of saturating their possible userbase, the rise of Tik Tok which they cannot just buy, and the Apple ad targeting limitations.

I don't know if that's true, but it's how I imagine other investors seeing it.

There is much more to that than just a new name. Facebook basically pivoted as a company. Now, if you have stock, you are an investor into a company with a different focus, different risks, different name, a different future, etc. if Google renamed the company to Alphabet saying that they will now focus on producing alphabet soup their stock would also tank.

Facebook renamed when they were only Facebook. Oculus is no where near big enough yet.

Google renamed the parent when there were substantial different activities occurring in different non-Google divisions. It made things clearer.

Also Facebook expects people to call it meta whereas Google basically expects to continue to be called Google.

Hmm hadn't thought of that. Did google have the same quantitative issues when they changes names or did that come a few years after? It could just be they timed their jump well.

That FB renamed to Meta in a bad conjecture while it was hemmoraeging users, whereas as the Alphabet renaming looked like a mere organizational refactoring in a constant growth context.