Because most people don't regard bitcoin as funds. That perception could change of course, or work for a different non traditional currency. The traditional thing to do is to have guaranteed convertibility until it takes off - I remember a story about Hong Kong having a jet full of dollars in cash to guarantee convertibility when the Hong Kong dollar was fixed against the US dollar, though I cant find any evidence that this is true...

How is that different from "let potential consumers of my service/app pay me"? Do you have to ask?

Unless of course you have an app that can survive of the (relative) tiny amount of people who use Bitcoin. You might, but you'd have to admit that you're an outlier :)