It's also not like the video's been a hit just for Starsector, it's been Sseth's second most viewed video right after the sides-busting SS13 one. I'd say it's a result of a valuable product in the hands of a seasoned merchant :3 A... mutually beneficial cooperation, so to speak.
As for me, I'm guilty of being a Ssoomer as well. Started following the warlord for his Deus Ex video, but the Starsector one was the first that ever got me to buy a game. I'd say Alex got exceptionally lucky with his approach, getting advertised by an exceptionally popular NSFW YT reviewer of obscure and outdated quality games is basically getting to ride a unicorn.