I don't think it's something for concern. Androids install base is huge, yet they are not capitalising on it through their app store. Admittedly, Google's main product is collecting data to make money from, so just having a huge install base makes them money, but still, a proportion of those devices are going to be things like smart TV's, IoT devices, and entry level things which will never make money for anyone.
Bottom line is, and I saw articles over the years how android just doesn't really make money for anyone. Even advertising on android is a black hole, since the advertising costs more than the benefit gained from advertising. This is something which MS needs to be able to address. They can't possibly expect developers to flock to making windows apps if they don't make money. This is something iOS does well. A lot of users buy apps, and developers support the platform well. There's 9 times as many android devices out there, yet in terms of app store revenue, google's is well below apple's, and when you combine all the other android app stores, they've only surpassed apple this year.
So tl;dr, it's quality that MS should aim for. Install base is not most important when looking at it on its own, other aspects play a role as well.