I understand your argument and it’s a potential reason. But single reason causal arguments are often overdetermined. Other plausible reasons are:

1. Community notes are more scalable.

2. Community notes are more accurate (check back in 1 year)

3. Fact checking opinions which most of social media is, is impossible. One person’s “truth” is another’s conspiracy theory.

4. Freedom of speech. Constitutional violation lawsuit avoidance.

5. Community notes are cheaper and Meta is a business.

6. It’s politics