Only targeting new hardware is just a win-win-win for them.
Hardware partners love it, planned obsolescence is just new sales. Legal departments love it, constantly worse DRM. The development teams like it, less support burden. Marketing loves AI being a core feature.
They have no competition. There is no downside for them.
I think they just mean they should have control over the modem. They are all locked down and proprietary with known backdoors throughout history, effectively bypassing any OS level security.