It's ridiculous thats what it is, plain and simple
Just like installing G.Fast at the cabinet, let's try and sell faster speeds to people who already have the fastest fttc speeds available. Unless it's priced very similar to 80/20 I doubt the majority will pay more for what they don't actually need.
nail hit on head.
I hated adsl2+ as it was the same thing, helps those always with a max adsl1 speed but not those on long lines.
cabinet based g.fast will have hindered sales as those who can get it will already have top end vdsl speeds, the speed cutoff will vary, but my line is just outside of BT target g.fast range and my attainable on fast path is currently about 66.5. I think it is no coincidence that the areas that filled cabinet's quickly are areas which had poor performing ADSL services, such areas are mine and ignition's. Ignition had to beg BT to get a cabinet, they were so wrong that his area wouldnt have the demand. My area was late in the rollout and filled up the cabinet quite quickly. Meanwhile isp's are struggling to get people on 15+ meg adsl2+ connections to upgrade to FTTC.
As ignition has pointed out before tho, BT are averse to capital expenditure, g.fast from cabinet's has minimal capital expenditure so they may not be too fussed if the sales are low.
Where the money is spent will typically be dictated by the following.
Subsidies - in this case not only has it produced FTTC, but a higher quality FTTC than the commercial rollout as it has vectoring and only hauwei cabinets no ECI.
Political intervention, the government wants the plebs who moan a lot to be satisfied so some leaning onto BT can get those areas sorted, notice most of the early FTTC rollout was rural.
Competition - if VM are offering XX speed, and BT can only supply X speed in that area, then that area will logically have higher priority for upgrades than an area which has no competition.