2) Even if they're backpedalling on the idea of macOS as a server and pushing for migrating to open source tools, they don't want to openly admit this, that always looks bad and unprofessional.
3) They're probably phasing it out slowly and in the next release or two they will probably deprecate it, and remove it completely from MAS in the next major macOS update.
4) They'll want to wait until they can play up their contribution and downplays that they were on the wrong side of history: "We're deprecating macOS Server, which has been a boon and a huge innovation in this space for 20 years, and helped $N millions of customers, but at this point the open source community has finally caught up to our quality."
5) At that point, the remaining useful features will be integrated into macOS proper for free, and they'll tout how they're benefiting everyone by doing this and simplifying everyone's workflow and saving everyone money.