Not always true. Especially for something running on client devices. You can't expect an app maker to own every possible device their code is going to run on.
Now maybe Google could do something like that, but 99% of people couldn't.
There's also, in this case, a question of if anyone is still using the device/browser/whatever. It sounds like they know removing the workaround will in fact break that use case, they just don't know if they should care or not.
The third party in this case might be Grandpa Joe. You can't exactly ask him to use the beta version of X and see if it's broken. Or if he's still on Firefox vOld.ancent.
It used to be that when someone got a fancy new device, like an iPhone you just said: - If you want me to fix the issues, send me an device.
Now alot can be emulated. I can for example start Xcode simulator and pick the device someone have issues with. Or I can run Windows Xp in VirtualBox. Or emulate the Samsung smart-watch, or run Android emulator. So a lot of devices can be simulated or emulated, and you can try removing a line of code and re-run the test suit on all the virtual devices.
Lots of old code for obsolete devices is only one end of the problem! The other end is to make sure all those old devices still works when you make changes and add new features! There's no idea keeping and old fix if the app will crash on that device anyway.
Now maybe Google could do something like that, but 99% of people couldn't.
There's also, in this case, a question of if anyone is still using the device/browser/whatever. It sounds like they know removing the workaround will in fact break that use case, they just don't know if they should care or not.
The third party in this case might be Grandpa Joe. You can't exactly ask him to use the beta version of X and see if it's broken. Or if he's still on Firefox vOld.ancent.