People underrate the homogenous culture that makes it easier to build something and have a large market that will consume it.
In Europe, for example, you have a much less homogenous market. A French retailer/business may be popular in France, but has a lot of friction going to another market. Not so much in the US.
So large, homogenous, wealthy culture that, if you can address a problem for, creates a financial foundation, and makes your app exist in at least a cultural context somewhat portable to other markets outside the US.
In Europe, for example, you have a much less homogenous market. A French retailer/business may be popular in France, but has a lot of friction going to another market. Not so much in the US.
So large, homogenous, wealthy culture that, if you can address a problem for, creates a financial foundation, and makes your app exist in at least a cultural context somewhat portable to other markets outside the US.