Android meant there was suddenly a purpose/reason to add an expensive component like a capacitive panel to the bill of materials. The proliferation of Android devices then brought the cost down of capacitive panels.
Why would capacitive screens be dropping in cost if the only widely licensed smartphone software at the time (Win Mobile) didn't even support them? That makes no sense.
Technology improved. Capacitive touch screens were out there generally in a larger format. Multi touch and capative screens have around since the 80's. Cost keep coming down. Apple used them because they had come down in cost, and worked well enough. They did not have to deal with legacy device like WM did.
Do not forget the screens have been around for a very long time.
That let them jump over to better tech.