This is happening with routers, too. Just recently had someone give me a new Netgear Nighthawk for free, and I was stoked until it wanted me to download an app and create an account to manage my network. Straight to the garbage.
Most products like this have some kind of "harder way" to set up without an account, while the smartphone way uses an account. For a router usually means that if you want the old-fashioned manual way you need to visit the router's gateway IP and set it up from there.
Sometimes "the smartphone way" even has a way around having to make an account, it's just that it's hard to find or discouraged. E.g., I set up my HP printer without an account or any ink subscriptions (and I even think it's a great printer, shocking, I know).
(I had a Nighthawk device relatively recently and it had no need for an account, but I don't actually know if this has changed recently)
Once that is done you can use the browser for a few things, but for WiFi password and all I think app is still needed. Couldn't find a way to do it other way.
Worst thing is that this stupid Xfinity app eats phone battery like crazy. So I had to disable background activity and bluetooth permissions once I was done with the activation and initial setup.
- my most recent Comcast/Xfinity experience