Trying to use your analogy I would say its more like taking your harley-davidson to a general motorcycle repair shop who won't work on it because its not a "real" motorcycle.

They might say that but wouldn't the case be that they're not serving Harley because they can't get the proprietary screwheads for it?

In the case of games, the issue might've been IP and fair use. "Not art enough" in IP law means you might not be able to pass a fair use lawsuit for it.

I went back and found their original post[0]. It looks like they changed their stance in 2014 because video games were "no longer an outlier in our community nor a drag on our resources the way it once was".

[0] https://vimeo.com/blog/post/new-upload-rules