.. Other suppliers are already in the head end exchanges, have the links there (for FTTC) why not offer an FTTP based service ? It's a good product, why limit what you can offer your customers ?
Two obvious reasons spring to mind:
1) As the number of customers able to order a Openreach based native FTTP service on the whole
are relatively very few, it doesn't make financial sense for the ISP to spend £1000s to train staff and develop ordering systems which will potentially benefit very few customers.
2) Based on some of the horror stories you hear about some FTTP installations by Openreach, it may be that Sky, TalkTalk, Vodafone et al don't trust Openreach to install FTTP within a reasonable (4 weeks?) time frame. Obviously in the case of FTTP installation delays, the punter will blame the ISP when clearly Openreach will often be the cause.
FluidOne FTTP On Demand 330/30 Mbps
Netgear Nighthawk X10 running Voxel