The weird thing is I've seen enough forks that have never seen any development that I'm pretty sure some people are using those as bookmarks rather than stars!
And forks on github have some bad ergonomics! Weird places where the upstream project still has control/influence over your fork. A full clone is better if you actually want control over the code fork.
I'm not a SWE but I use github still, I thought stars ARE bookmarks, what are stars then???? They're not for bookmarking????
I would think most people use it for bookmarking, but it seems like another portion of users use it as a "like" button.
It is kinda both. It also reposts the project for your GitHub followers.
They are currency of reputation and status. If you have enough stars, you get invited to private parties with elites. (I am just joking, they are bookmarks who got famous)
Nobody knows but since we are at the point where you can get VC money if you have enough, there is an incentive to get them.
AFAIK the "fork" option also helps guard against the original project getting deleted or somehow moved.