I think there are probably 3 main reasons people are slow to choose FTTP
1. As mentioned before there is confusion on what FTTP is. I know multiple people who bought an FTTC connection and thought it was FTTP. My neighbour when I told him dropped Sky FTTC and signed up to VM. I suspect many won't know the difference between full fibre or fibre to the cabinet, so there is no incentive to change.
2. ISP's selling products that are FTTC seem to be reluctant to undercut those products in favour of promoting FTTP products. So there is no general advertising of FTTP products unless its available in a specific area.
3. As pointed out by some posters on the thread, as long as people can do what they want to do on their current service without any quality of service issues then they won't see any reason to even look up faster connections. They will likely only look at the speed difference and not realise the overall quality of service. I bet many think they are getting the top speed on their FTTC connections, as I doubt they look up what speed they are getting.
BT Infinity 2 - ECI Cabinet