WeTek's business is focussed on the OTT middleware market and they (and most similar manufacturers in that market) are making a strategic shift towards AndroidTV as that's the direction Google is pushing everything now. As such the latest generation of their devices are not using AOSP and the boot process is locked down per AndroidTV spec. I swapped email with the CEO on this topic a few months ago when the next generation of 'Hub' sized box was announced and WeTek have no plans to release 'Linux' versions of these products.
It's also a market trend that will continue. Over time more manufacturers will become AndroidTV only and the number of manufacturers with AOSP products will concentrate on the low end of the market with cheaper manufacturers who source lower-grade components and take more design short-cuts to increase their profit. This long-term reality is one of the reasons why LibreELEC started to focus more on SBC "board" devices where the manufacturers are invested in Linux support than Android "box" devices where manufacturers are not, and where we see significantly more end-user support issues. Boards aren't as cheap as boxes, but at some point users will realise the experience is much better.
NB: WeTek delivered Netflix 4k support on Android. It was never promised on Linux. One of the "lessons learned the hard way" with dual OS support is that users read the spec for one OS and blindly assume the other OS works the same. It was never the case and WeTek burned a lot of support man-hours dealing with people that can't read. It's definitely a factor in their decision to not release more Linux devices.