That's perhaps what the developer told you but OpenReach have offered free FTTP for developers for quite a while now.
Free on developments over 250 homes since early (march?) 2016.
Reduced to 100 homes in May 2016.
Reduced to 30 homes sometime later in 2016.
Prior to these dates the developer could contribute and pay for FTTP instead of copper, and some did just that.
Most didn't.
It wasn't a priority as people were still buying their new homes for hundreds of thousands with access to only ADSL broadband.
AFAIK, Openreach couldn�t provide fibre at the time of the original quote for our phase of development, so we got copper Exchange Only lines,
I've never seen a quote say "couldn't provide fibre".
I suspect that the decision to give us EO lines was always predicated on a future fibre upgrade
Not OpenReach's decision.
Your developer most likely didn't want to pay or didn't engage with OpenReach at all on FTTP and that means copper is installed as standard.
OpenReach deliver what the developer orders.
There's probably a dozen new build estates being built in stages within 5 miles of me.
Every single 1 has copper in the earliest deployments, with most of the later phases being FTTP.
In a couple of these developments the developer has paid OpenReach to retro fit FTTP for the early phases who had copper and now they have both.
Developers have had the option to pay for FTTC cabinets for years also.