Of course I know the reason - that's because my machine is memory constrained, I routinely run on ~90% RAM usage. But hey, that 8GB of RAM isn't here for vacation, it's to be used.
Personally, I find the mobile app lifecycle - which is where they took the idea from - to be incredibly annoying. I like to have control both when applications die and when they start up (which, on Android, is utterly unpredictable).
I have a "metro" style SSH application, and windows regularly decides it should close it, which kills my active SSH sessions.
I understand that they removed the ability to opt-out to force developers to change to a more appropriate model, but there are cases where a task cannot be suspended (because, for example, it's interacting with another computer). Having to re-log-in to my ssh session the 4th or 5th time in an hour is absolutely infuriating.
The support for background processes continues to improve. Windows 10, for instance, now supports a "single instance" background processing model where background processes can be seen as an invocation of the UI app (if already running) and vice versa (the UI app is presented as an invocation to the background process if that is already running) with hand-offs from one to the other, simplifying the programming of some of the interactions between background and UI for some apps.
The complaints about this lifecycle model from app developers is that is hard to program for. Windows 8 was also strict enough forcing this lifecycle (closing out applications sometimes seconds after minimizing and attempting to restore them quickly on window restore) that it showed how bad developers can be at programming hard things like proper app lifecycle management, so they begged Windows to be less strict about it.
(That was one of the magic things about Windows 8 that Windows 10 doesn't quite replicate: minimizing a properly built application and watching the application's memory and CPU usage quickly drop to zero.)