It’s not just that the brightest at Microsoft or Nokia or Google can’t make an upgrade stick. It’s that the upgrade is not universally beneficial to the value chain. To remedy this, licensors have to resort to contractual obligations to ensure upgrades, but enforcement is non-trivial and can lead to aggravated relationships.
Phone makers (Nokia, HTC) are interested in making their phones better with upgrades. Phone OS vendors are interested in getting their latest OS on most eligible devices possible.
Yet, the parties controlling these upgrades are phone carriers. Their interests lie in getting customers to buy into their next contract. Making the experience they have with their current phone better comes way down in that list.
Slight conflict of interest.