I don't disagree, but things are pretty complicated, much more so than they might seem from the outside.  First, if the configuration isn't stored there's literally no way to have a backup for most of the CPE vendors so there's definitely reason to have it duplicated in the service providers' systems.  Very few allow for end users to download their router configuration via the admin page and I know of none that encrypt that configuration before it is delivered to the end user's computer.  (It's also relevant that the usage for those vendors that do allow end users to backup the config is vanishingly low.)  If we're looking at a TR-069 based system for managing the WiFi and router components it's not really feasible to do a real time grab of that data since that process can take up to ~5 minutes depending on your periodic inform settings in your ACS.  That's because TR-069 is inherently a push technology (from the CPE to the ACS) rather than a pull like SNMP.

The next piece is that a DOCSIS configuration file itself, which in some cases contains these parameters, is by the standard required to be delivered via insecure protocols, namely TFTP.  Newer devices have options to allow for TLS secured HTTP, but that's very rare today in production provisioning systems, and in case the secured protocols are all still optional in the spec.  In general the config file itself is stored in it's text format on the provisioning systems or if the file is dynamically generated the user specific parameters are held in a database with the general ones coming from a template for that class of service.

Again, I'm not disagreeing with your premise but the service providers directly control a small piece of the overall process and we're still working with standards from earlier times.  Most cable operators have gotten rid of their DOCSIS 2.0 (1.0 and 1.1 as well) but it's not uncommon to find a handful of users with (mostly customer owned) D2 devices that the provisioning and OSS systems still have to deal with.  DOCSIS 3.0 devices are the majority and 3.1 devices are just now being rolled out in large numbers.  

In short, not everything is quickly retrievable, much of the configuration is in fact generated by the service provider and must be maintained because the modem needs to download its configuration every time it reboots, and the vendors and associations in the provisioning and OSS space have more input than the operators themselves.