Consider, a single-engineer company with an interesting app and talented engineer, just how much do you expect to be acquired for? Recognize that a $1M-2M offer is about what you could make in 4 years at Google at the appropriate level and with the appropriate amount of restricted stock units.
So, if the amount of compensation would be approximately the same, but the one pathway (acquisition) requires a lot more legal groundwork and expense, and the other doesn't (just extend an offer of employment with generous signing bonus)
I think there's a little bit of ego involved here. It's easy to believe you have a winning app that's going to be huge, and be insulted when other people don't see the potential. ("A mere engineer!? Me?! I'm an entrepreneur who should have more respect!"), but the reality is, very few apps on the app store take off like rocketships, most fail, and so unless you have unique very valuable IP, or have built up a lot of valuable data, chances are, most companies are going to view it as an acqui-hire.
Paul Graham was right, you talk to Corp Dev if you're very successful, or nor very successful (probably going to die). As Kenny Rogers said you've got to know when to fold 'em, and this could have been a situation to negotiate a nice big fat signing bonus.