Have you seen any OR staff or contractors pulling out "old copper cable" en-masse or even individually, after an upgrade involving "Fibre"?
Taking FTTC/VDSL upgrades (which are the vast majority involving Fibre), the existing copper cable (plus the new double copper links between the PCP and the FTTC, are essential for maintaining the "traditional" phone services; and also that length from FTTC via PCP to your house particularly so for delivering the VDSL.
Additionally, the majority of the existing phone wiring is carried from the exchange to the PCP by multi-way cables, something like 100 pairs, so to unthread one specific pair for removal is well-nigh impossible.
And at the most recent BT Report I am aware of, on average only 21% of users to whom it is available, 80 to 90%, have actually upgraded to a Fibre product.
So very far from "we are all now on Fibre where Fibre is available!"
Observation of "my" FTTC (10 Metres from front door) and PCP (50 Metres) apparently confirms those figures.
288 VDSL "lines" pottentially available in FTTC
96 with Filter Links actually in place in the FTTC, so "immediately available for use", subject to any other required, remote action.
About 300 existing "old copper" lines in the PCP, extrapolated from Postcode coverage, at very most, only up to 96 Users have upgraded to VDSL
Originally only 48 Filter/Links were fitted in the FTTC, with another 48 added in June 2015.
The FTTC has been operational since March 2014.