alt Hacker NewsThat's definitely a feasible explanation (and the one I would assume to be true for AliExpress).
But there is another, slightly less evil, explanation that I know at least some companies have pushed their apps because of: the thinking is that if you're on their website, there is less friction to open a new tab and search for a lower price from their competitors, than if you're in their app. Obviously it's hardly any different - opening a new app (the web browser) vs. opening a new tab in the app you're already in - but the theory is that there's a slight psychological difference.
Of course I'm not saying that trying to prevent your customers from searching for better deals is a nice thing to do. Just adding that data mining isn't the only reason for some companies to want people to use their apps.
It's quickly getting to the point for me that "find the thing I want locally and buy online if it's cheaper" is reversing. I've actually been to one of the few remaining electronics retailers to look for a PC for my kid recently, and it was nice not to be assailed by dark patterns (yes, there are dark patterns in b&m retail, but they're much more obvious).