Distrowatch's source for popularity is how often the different distros are clicked on on their own homepage... which has the toplist featured prominantly on the start page.

So their ranking completely and utterly worthless, as it's prone to manipulation and once you basically pushed your distro to the high spots it's guaranteed to stay there as a rarely used but highly rated distro is of course attracting more clicks from people wanting to know what it's actually about... see: MX Linux being on their #1 spot forever.

Its insanely popular on distrowatch. I also don’t know why

Distrowatch counts clicks on Distrowatch. People using methods like setting the distro page as new tab page or perhaps even use scripts to boost awareness of obscure distributions is a regular occurrence. Nobody can seriously tell me that PCLinuxOS having been on the top of the DW charts for a long time (it's still ahead of Kubuntu, Genoo, and RHEL) is because of how freaking popular that thing is. I'm also very doubtful of the current popularity of MX Linux over there. No way on earth is that seriously 2.5 times more popular than Ubuntu.

It's what Ubuntu once strove to be.