1) No more carriers. They get a consistent, high margin monthly revenue stream, can have one worldwide SKU and can let illegal imports take care of situations where there has been the potential for bans e.g. patents or Russia.
2) No more dealing with Qualcomm and 5/6G standards bodies and having them dictate where the industry goes.
3) Further ties customers to Apple in a world where its getting harder to differentiate on hardware features alone. Instead they can differentiate on the network e.g. no more roaming charges and offer unique bundles e.g. ATV+ with Apple Internet. And good luck with smaller players being able to launch their own satellite.
4) No more dealing with foreign governments blocking websites, demanding apps be installed, intercepting traffic and by extension far less jailing and killing of dissidents, minorities, journalists etc.
5) Apple owns the total experience. It's just you and Apple.