Investor desires congeal into a messy influence on the company. An investor pushing on the company helps direct that blob of influence a little bit.

It’s like when you’re annoyed about something local government is doing and you show up with 50 other people also annoyed. Now you’re part of a news story and a stakeholder faction. But you all got there because of your individual desires.

Also, the letter is a public artifact. The investor is also meeting formally and/or informally with Google or individual directors.

Publicity stunt.

It’s not like sending a letter cost them anything, but now they are famous.

They do actually want people to act on their letter. This is the same as an analyst in an earnings calls saying "hey can you slow HC growth even faster?" They've got an opinion and put it out there.

But there is no evidence that this change is related to their letter (especially since none of the changes made in this case match any of the specific requests in the letter).

People read the letter and think they have more power than they do