> Furthermore, why is Session's page on the Apple App Store not a valid source for the claim that Session is available on the Apple App Store?
Because that’s a primary source which Wikipedia tries to avoid. Obviously this can get quite weird, but good luck arguing with a wiki rules lawyer fixated on that. People are often more reasonable than that though.
There are a lot of details that don't seem to get covered in secondary sources that a snapshot of a primary source would be better for anyways.
If I'm writing an article about you from scratch then I'd want to look for sources, to see if you're notable - etc. But if I was updating an existing article and just trying to find a source for your address it would seem easier to take it from your website than wait for a third party to write about it. At some point ideological purity gets in the way of practicality. And there's no need, you could easily tag first-party data so it could be audited and replaced.
Because that’s a primary source which Wikipedia tries to avoid. Obviously this can get quite weird, but good luck arguing with a wiki rules lawyer fixated on that. People are often more reasonable than that though.