This is based on Semmle, which they acquired last year. According to their docs (https://help.semmle.com/lgtm-enterprise/admin/help/sys-requi...) it supports C, C++, C#, Go, Java, JS, TypeScript, and Python; no Ruby. (Edit to add: Woops, missed that this list is also literally on the page. I had even looked first.)

It's really hard to do any kind of static analysis on something like Ruby or Perl where 1) you need a ton of context just to parse it properly, and 2) tracing calls is a nightmare. Given that, I'm completely unsurprised they haven't supported it yet.