Infill meaning they cherry-pick specific areas that need improvement but NOT with an aim to do everwhere on that exchange?
I added the bold.
It's more about cost per premises to pass with FTTP and not much to do with areas that need improvement.
Most infill FTTP work is simply cheap and quick to reach, which tends to be urban areas.
These areas usually have at least SuperFast speeds already.
My area is not Fibre First or BDUK work and I'm getting FTTP.
Every single property getting FTTP already has FTTC over 30Mb/s with most nearer 70-80Mb/s.
Every property getting infill FTTP around me has just had Virgin rolled out to the area.
This is more than likely part of the reason for OpenReach doing FTTP, competition.
The fact my area is new and fully ducted makes it much cheaper for OpenReach.
At the end of the day OpenReach is a private company out to make money.
They will continue to roll out to the cheapest/easiest to reach areas.
They will hold off for funding/subsidies for areas that are not commercially profitable which says often areas that actually need improving.