If you have a load of copper and fibre converging on an exchange, how do you make it all go away if you want to cash in and turn the exchange into residential housing?
I haven't been actively involved in telecoms for a while but as an example you can just look at how Openreach are implementing the rollout of FTTP/VDSL.
Many small exchanges are not being enabled themselves, but their cabinets/fibre nodes are connected to headends at larger exchanges. This means these smaller exchanges can be 'bypassed' in the long term.
The fibre infrastructure feeding the VDSL network has spare fibres ready to support an eventual GPON FTTH/G-fast rollout.
There will still issues to be resolved - for instance:
1) 999 services;
2) powering lines in a power cut;
but if/when BT switch to VoIP in the local access network and carry that traffic over fibre rather than copper than the smaller exchanges become less important/eventually redundant freeing up those locations.
As I said, I believe its a long term strategy.. its not going to happen quickly.