Cyanogen basically lives on as LineageOS. It died because of internal conflicts.
Why did they all fail? Because of the chicken/egg problem that users require apps but app developers require a user-base for a platform to be economically feasible.
Apple/Android were able to succeed (and take the market from e.g. Symbian) because of a shift in mobile market (the capacitive touchscreen).
So we need another revolution (“big change”) in the market. What will it be? Can the GDPR be a driving factor? Is Microsoft rooting for a coming back eventually? Perhaps PWAs are going to allow better cross platform apps since that lowers the gap of entry?