A few days ago, in response to my complaining about all the reviewing I’ve had to do lately, an undergrad researcher friend asked me, “what’s the incentive to sign up to join PCs and review papers? it seems like a lot of (free?) labor.”
Good question! Here are some reasons why someone might sign up to review academic papers. TL;DR: you should review papers in order to: provide a crucial service to the community; see a preview of new work in your field; advocate for the kind of work you want to see more of; build a reputation; see and learn from what other reviewers say; get better at writing strong papers yourself; better understand how arbitrary acceptance and rejection decisions can be; and feel good.