Reduce the number of API requests from whatever 3rd party apps are left; this reduces server load and costs.
Coerce users into trying the 1st party app and tolerating it so they can watch NSFW content. This may cause some users to abandon the 3rd party app and just settle for the 1st party app.
Only if it’s a specialty filament or something tricky; like Proto-Pasta can be. If I’m just running another spool of Hatchbox or Overture I just use my generic PLA profile and send it.
The point of this is to:
I doubt it has much to do with advertising.