Because the average user and the vast majority of users can't use your straightforward and easy UI without explicit instructions because they don't understand any of it.
If they're not going to use it or understand it, why spend time on it?
The model is moving to ISP-controlled network hardware anyway.
All new Comcast modems are remotely manageable by Comcast and they enable features that customers have to call Comcast to disable, as Comcast has better access to the modem firmware than the end user.
It's actually irrelevant who uses the interface - the end user or ISP employee acting on users demand. Such change of the party in charge neither adds any usability to user interface (just the side who has to struggles with it), nor it increases security and reliability.
I actually believe that you're using false equivalence to pretend that both paradigms are the same. I disagree that they are, and I believe that you've made a lot of assumptions to declare my point "irrelevant", the biggest of which being that the software is identical and the only difference is who accesses it. That's a falsehood, and I'm going to reject the rest of your point because I disagree with those assumptions.
If they're not going to use it or understand it, why spend time on it?
The model is moving to ISP-controlled network hardware anyway.
All new Comcast modems are remotely manageable by Comcast and they enable features that customers have to call Comcast to disable, as Comcast has better access to the modem firmware than the end user.