Why BT is not upgrading Exchange Only (EO) lines to supply fibre optic?

To enable exchange only premises or houses to have high speed fibre optic internet connection, all BT has to do is install required amount of green street cabinets with required hardware for fibre optic enable services within the exchange premises or just outside of the exchange building and connect all exchange only lines to these cabinets. It is not major job nor does it cost vast sums of money. Planing permission may be needed from local authorities but generally there are no barriers.