Every business decision carries risk. The question is whether or not the risk is acceptable.

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.)