However I don't see an issue with them developing screens with a higher PPI despite them not being strictly necessary with regards to phone displays, as it's all about technological progress, this is where the sort of screens that end up in future versions of Occulus Rifts start out
I disagree, implementing higher ppi displays in situations that don't benefit anyone and are constrained by very limited power source is just purely wasteful.
It's done for simple marketing power.
The fact that you can get 440ppi in a 5" phone already suggests that 440ppi could be done on a 7" or a 10" display.