BT Openreach provide Fibre to the Cabinet to some homes and Fibre to the Premises to some others. The roll-out of these services is in two phases.
The phase that BT Openreach are funding themselves, called the commercial roll-out, has almost finished and the final areas have already been announced. BT Openreach paid little if any account to expressions of interest in this process - they installed wherever they felt they'd get the best return on investment.
The second phase is where BT Openreach are rolling out with some public money via the Broadband Delivery UK projects. These contracts are awarded on an area by area basis, with the available funding being targeted to maximum effect. Part of BDUK is a minimum service obligation of 2 Mbit/s, but your connection already exceeds this. It's possible that you will not receive FTTx from this phase, either.
The only expressions of interest that BT Openreach will listen to are those accompanied by a commitment to provide a substantial sum of money. It seems they typically want £30,000 to add a cabinet to their FTTC roll-out programme.
FTTP On Demand is limited to areas where FTTC is already available. If it remains at its current pricing when fully launched, it will remain a niche product.
The harsh reality is that fibre roll-out is expensive, and it is uneconomic to cover everywhere.