Presumably because the `larger mapping infrastructure` doesn't deem a filterable list of pinball machines to make monetary sense, or fit into their overall product without adding clutter.

I presume the same is true for the IMDB. They have their own list of things they are interested in, and firearms or cars may not be on that list.

It's almost like different people/organizations have different interests and priorities.

It's easier to build a community when you're running your own site. Also, it's just easier to get started. You don't have to figure out someone else's data format and object classes if you just start from 0, and most people working on these kinds of niche hobby sites don't always care what an object class is anyway

Is there an internet movie song database? I'd like to look up a song and see what movies and tv shows that song has been in. I thought I saw something like that many years ago... but wasn't exactly what I wanted.

because the pinball map serves a purpose that would not fit well in a larger mapping thing. people want to know what pinball machines are nearby them so they can go there and play them. very different in scope than a movie gun/car database. they also don't share the same playerbase that a more general arcade machine app might have; people like pinball and will seek that out in a different way that people who like arcade machines will not do the same.