I'm not sure they should be pre-installed at all.
One of the advantages of an app store built into the system is that it's trivially easy to add the stuff you want from the store. If someone wants to play solitaire they could easily find and add it in the app store.
Fact is, Microsoft don't have any confidence in their own store and the constant shovelling of this stuff onto PCs in the way they have been proves that.
Interestingly enough, they're putting more weight behind command-line accessible app repositories like chocolatey for installing apps.... another good idea 'borrowed' from Linux. (Just to be clear, Chocolatey isn't a Microsoft project, someone else started it a while ago, but Microsoft are adding support to make using it easier in newer versions of Windows.
It was quite nice to rebuild my PC last time by just doing the normal windows install then running a powershell script for all the apps (https://itsalwaysmyproblem.com/2017/09/09/easy-pc-rebuilds-with-chocolatey/)