When I look at Mastodon posts, I see a decent amount of replies and boosts for popular posts, but not very many stars (see example image). I assumed a star is the same as a like, but I feel not a lot of people star a post, whereas I did see a lot of hearts/likes on Twitter posts. Are they not equivalent?
No. You will only see comments by users who have at least 1 follower on your local instance, at least in the official UI/app.