It powers lichess.org, who have made multiple blogposts about how happy they are with it.
Lichess is a FOSS chess server that somehow manages to compete with chess.com proprietary, distributed, milticloud kubernetes setup from a single VPS. According to them, scala helps.
Because the extensions replaced wordpress' sitebuilder/editor. If I were to get rid of the extensions I would basically have to recreate the site anyways so I might as well switch away from wordpress.