Mainly since employers expect you to have a high degree of competency on the stack they are seeking people for. Sure I have worked with other languages like Python and Go, but I don't have the breath of experience I have on Ruby or C#... I guess I picked the wrong languages =)

I think you picked wrong only in narrowing yourself so much. Nobody cares about your deep language knowledge unfortunately, unless that translates into more velocity. It's not pretty but it's what it is. For someone to care about your deep knowledge it needs to be at the level of writing books and being involved in the specs, with commit rights to core, and even then...

This isn’t true - many hiring managers and HR filters do in fact screen by language and keywords. I personally wouldn’t work there but it’s particularly true for non tech companies and especially true for sweat shop like environments. A lot of Java and c++ roles are also very specific in what they’re hire for because the frameworks and (in c++ especially) language complexity is profound. A competent ruby developer would take a decade to become a competent c++ engineer because it takes a decade to really learn the complexities of c++ at that level. (Which is one reason I’m a huge supporter of rust killing off c++). Companies built around modern tool chains tend to be more progressive in their hiring and their tool chains are more forgiving.