Google maps is no longer good for hobby projects as the free tier is so low.
It's like they're trying to drive away everybody but but big enterprise shops.
Mapbox's free tier only gives 50k map views, and only for non-commercial apps. If you're a paid app, you also have to pay $499 per month on top of your usage.
I like what they're doing, and wanted to use them for a web app with restricted access, but certainly not going to pay $499pcm for a side project.
If you don't want to serve any customers making under $10M, then other companies serving those customers are not your competition. At least not today. Is there a risk they might take their broader customer base and use it to compete with you upmarket some day? Yes. But that's why you do things like build a brand, relationships, technologies, and other competitive advantages within your niche.
Fancy steakhouses generally don't worry about McDonald's. (Not that this is a perfect analogy to Google vs MapBox. Just speaking generally here in response to your general point.)
Didn't that happen just a week or so ago? I don't think this can be attributed to the pricing change this early.