I responded to what you said, which was doubting the value of the latest versions and being stuck with old keyboards and dictionaries.
The platform's fragmentation is the biggest problem by miles. It's hardly Google's fault - manufacturers bloat up the AOSP software so severely that it takes a huge amount of effort to repeat the bloat every time a new version of Android is released. So naturally they're quick to abandon older hardware. If consumers voted with their wallets and bought phones with vanilla or close to vanilla Android on, the big boys like Samsung and LG would be forced to cut their crap (progress has been made on this front already in fact). Which might greatly reduce the effort it takes to keep their devices up to date.
It's one of the three reasons I love OnePlus so much: 1. Insane hardware 2. Affordable price 3. Basically vanilla Android. Pure heaven.
Obviously the ideal situation is Google suddenly declaring that AOSP Android is how it must ship on all devices, but that is guaranteed to cause a major s**tstorm so it won't happen.