They already have an ad platform, they’re expanding it a bit. It’s not like Google or Amazon in that it’s not a general ad network that you would use for web sites, stores, etc., it’s more like a software library you can use to easily make ad funded apps for iOS, and advertisers can buy ads in search results, the mobile ad platform, and I think probably their music radio thing.
I am actually pretty excited to see where this leads. They have been pretty safe so far with just hardware and OS as far as widespread user anger (yes not always) but now they are exploring other revenue stream, how far will they sink and what mistakes will be made?
Apple did this for 6 years with iAds, but they never got their act together as they’re pretty terrible at online services when compared to Google, so it shut down in 2016. This is just their second crack at it.