The only problem with this is that having such a complex function as a non-core business unit makes it ripe to get rid of, or try to find a way to make it a profit center.
Cloudflare, for example, removed the ability to change the nameservers for all domains registered with them.
Google got tired of being in the business and sold it to Squarespace.
Being a domain registrar is a total PITA and is not for the faint of heart, so it's the sort of thing that any business that takes it on as a non-core function will eventually tire of.
> Cloudflare, for example, removed the ability to change the nameservers for all domains registered with them.
Cloudflare never offered that ability. From the time they started offering domain registrations, it was always with the caveat that the nameservers would be fixed to Cloudflare's.