It's not uniformly available in the US either. If the local transit authority publishes the data in the right format, then Google will add it to their maps. I suppose if there's sufficient interest they might write a custom scraper.

My local transit authority thought this was a better idea: http://www.katbus.com

in many cases they can't offer it because the transit authorities do not wish to provide that data to Google.

I'm not saying it's Google's fault (I know it very likely isn't). steevdave opened the door to other people's experience re. mass transit on Google Maps versus Apple Maps, I gave mine.