@cody I think for me it's the quantity of developers willing to work with a technology. JS has a ton of terrible code out there, but people love working with it, and there's a lot of incredible JS developers out there. People flock to learn that technology because it's solid, easy to use, and generally enjoyable.
As a JS / Java dev myself, I came here assuming kbin would be a JS project, and when I learned it was PHP I immediately recoiled. Not because I personally hate PHP, but because I don't know the technology (or many other devs who do) and found it interesting from an OSS perspective because there's (in my world) less dev resources available to help maintain a PHP project.
I agree though, build something in the stack you know. If @ernest likes PHP and that's where he thrives, it makes sense to do it there. PHP people will come to assist. Or you might get people (like me) to maybe rethink their perspective, because I'd love to help out here, but it's gonna be a new experience for sure!