VM aren't building the network, they've agreed to purchase wholesale services on it. PIA rates are Fujitsu's problem and their fight on this one.
You're dead right PR is a big driver behind the announcement, they are trying to get their hands on some of the
BDUK funding. In addition this is to put some pressure on Ofcom to force PIA rates lower.
Some well clustered rural areas are actually cheaper to enable for FTTP than urban areas due to less complicated civils within the home, less MDUs, easier access to homes, etc.