I kinda look at Openreach as having an ongoing internal battle between an FTTP faction and a copper faction, with the accountants as a referee.
The FTTP faction are permanently up against it, trying to persuade the accountants that their costs have reduced enough, and this time they deserve a bigger chance. They are constantly having to adjust all manner of techniques to reduce costs ... and the BT release that was the background to ISPreview's story highlighted that they'd managed to halve FTTP installation costs.
Trials like this, then, are ways to prove that all these techniques, taken together, do provide an accumulated saving for at least one use case. Each trial helps persuade the referee a little more.
The G.Fast faction has a similar problem...
Historical aside:
I've seen one GPO document from 1965, that was the analysis of how the cabling & network deployment costs were changing since they'd chosen to start using a PCP/SCP model 20 years earlier. 20 years!
It takes time for engineers to gather evidence & persuade the accountants.