It shouldn't be preinstalled, but it should be easy to find professionally reviewed applications for the most common user application categories. Android's Google Play Store has "editor's choice" for example. If Ubuntu is trying to be THE desktop linux, this is something they should be doing.
Because even if Ubuntu knows that, users often want conflicting things.
User A may want a weather app preinstalled; user B may not want their computer knowing their location. User A and user B might even be the same person.
And that's assuming Ubuntu knows it, which let's be real, Ubuntu isn't great at knowing what its users want.
And all of that is assuming it's even true that most people do want a weather app.