The trouble is, from the point of view of basically everyone producing those devices, the current "what will every browser do this week" situation is not a viable platform to support in the traditional way. They can tell you their box works with certain browsers that are available at the time you buy it, but why is -- or should -- it be their problem if they supply a working product and then someone they have no control over updates a browser they didn't know you were using and something breaks?
If admins don't like this, they need to expect to pay a huge amount of money for ongoing support contracts that actively update to support new versions of browsers, or they need to stop demanding web-based config interfaces and get used to installing native software that uses proprietary protocols that will reliably still work next week as well.
The idea that vendors of devices that often have working lifetimes of 5-10 years or more should be responsible for keeping up with every little browser update for every "evergreen" browser throughout that lifetime as part of routine support is just not commercially viable, and that's why approximately no-one offers it.
