FTTPoD installation connects to your nearest aggregation node which also serves FTTC cabinets so if there are no cabinets then there won't be an aggregation node to connect to.
Not always.
There's many cases of EO lines that are within reach of an Agg Node and even cases where EO lines are right next door to properties served by an FTTC cabinet.
Probably EO lines that are a stone throw away from an Agg Node.
There's no technical/logistical reason why FTTPoD can't be delivered to an EO line.
The existing line and PCP aren't touched for FTTP.
It just appears to be the simplest way to offer FTTPoD to every property covered by an Agg Node while excluding rural/unviable properties.
It's a very crude method of doing it and it excludes a fair few EO line properties that are very much within reach of an Agg Node.
OpenReach records aren't great at the best of times. It might be quite a challenge to make FTTPoD available to specific EO lines while excluding others so they went with the easy option of mandating a line must be served by an FTTC cabinet.