I think that given the lack of market share, and constantly bad PR, it's everything forming this contagion, with apps and hardware being the two cornerstones that are polluting anything else from being done or invested in.
No one who pays attention to smartphones is going to recommend a windows phone. The advantages of the platform are so few, and so subtle, and so insignificant compared to the disadvantages, that it's quite seriously a non starter.
I think what ultimately killed it was the schizophrenic reboots, throwing early adopters and app developers under a bus, so to speak. From an investment point of view, everything MS did encouraged developers to do nothing.
Bottom line is, the platform needs more users, it needs a compelling case for investment from developers. If it can be shown that developing for the platform makes them money, they'll do it.