I'm not sure, but I can imagine that the reason why they didn't handcraft that many points of interest for the US (only 12 according to the map) is that almost every bigger city has photogrammetry (277 in total) and so POIs are already part of the scenery. Dallas and Washington DC are an exception.
I don’t know what their reasoning was, but photogrammetry coverage might have played a role here. In Asia, for instance, there was not a single city with photogrammetry before the Japan update but well over 80 handcrafted POIs (now it’s 104). In Europe many major cities do have photogrammetry (52), but still nowhere near as many as in the US. This would explain why there are more POIs in Europe (40, 12 of which in London and Paris). But this theory only holds for North America, Asia and Europe, as the numbers below show.
Here are the numbers of POIs I counted on the world map (no guarantee that it’s all of them) and number of photogrammetry cities in .
Asia: 80+ before the update (not 100% sure) [6 after Japan update]
Europe: 40 
Africa: 16 (12 in Egypt) 
North America: 12 
Middle and South America: 6 
Australia and New Zealand: 3 
Cities with 2 or more POIs:
Cairo: 8 (depending on which pyramids you include)
Tokyo: 8 (before the update, but not 100% sure)
Hong Kong: 7
NYC (photogrammetry): 4
Kuala Lumpur: 3
Washington DC: 2
Rio de Janeiro: 2
Based on these numbers I think we can see that there is a certain focus on North America, Europe and Asia, which probably is where their biggest markets are. I understand the frustration of some who like to fly in other regions (or Washington) to some extent, but the great thing about this sim is, I think, that this doesn’t mean that other regions look bad. Not at all. Much of Africa, for instance, has excellent imagery. Moreover, this is an ongoing process and I’m sure we’ll see some great updates in the future that also cover areas that previously weren’t given that much attention.
Back to your question. Since they only had the resources to model a limited number of POIs (say 200), they may have come to the conclusion that it made more sense to focus on regions that aren’t as well covered by photogrammetry as the US and thought 2 POIs for Washington were enough.