Sure, I understand what you're saying... but hosting requires a domain name. It's not an option. You have to have one. Every single customer also has to purchase/transfer/renew a domain name. And if they don't do their domains through us.. then they'll do it through godaddy, namecheap or some other popular company that also offers hosting along with domain stuff.
In other words... if you're a hosting provider and you also aren't offering domain names to your customers... you're basically pushing them into the arms of another company who is practically guaranteed to be constantly trying to upsell hosting to your customer.
Why would you do that?
It's a little bit like an oil change place for cars. Sure, you can create a business that sells ONLY oil change. Nothing else. But why? Not only can you make extra money selling things like transmission oil change, light bulb replacement, engine cleaning, etc... but if you don't.. the potential customer is forced to go somewhere else... and that other place is also going to sell oil changes. Pretty soon your customer will decide it's simpler/easier to just bring their car to one place instead of two.
I do not view hosting and domain management as two different services. They are two essential services in the same industry that go together. We don't just sell "hosting"... We sell hosting "service". And that includes domain name stuff, since it's absolutely required for every hosting customer.
I have the same opinion about SSL certificates.... Any "hosting" billing app that doesn't include full featured SSL sales/management is not designed well. Why would you purposely not sell a service that will force your customer to find the arms of a different lover?