They are obviously going for a Low Level Cap because they don't want to work on the content they would have to do if they went as high as 20. That's the sole reason but no one would come out and say it as it is. Like i would care waiting 3 years as long as they did all Content but i'm not handling their Deadlines nor Budget either.
personally i see it as they're already planning expansions, because everyone does these days.... create a game then break it in to dlcs for more money instead of making a product worth the money.... they don't even need to worry about manufacturing costs anymore, or ensuring a game is finished before release and that's the mindset. If there's a problem we might do something about it after we have their money, not we have to make sure it's as good as it can be or people won't buy it and we lose money.
Comes down to the ambivalent mindset of the consumer becasue they figure if it needs fixing they'll fix it instead of there's no way to fix it, like it was before the internet, and development has been half arsed across the board since.
