There's a few reasons for this. A big reason for adding the G.Fast pod to the PCP and not the fibre twin is it means the tie cables are measured in inches rather than many metres (over 50m in some cases). G.Fast is much more sensitive to distance of copper. G.Fast can also be installed on PCP's with no fibre twin.

The G.Fast pod is installed to the right of the shell. Both the fibre cabinets now used by OpenReach (big Huawei/small Huawei) can be expanded by adding extensions where the G.Fast pod would sit.

You say G.fast can be added without a fibre twin, which is possible, but unlikely, given close proximity of fibre and power already available on a PCP with a fibre twin.

Not sure what relevance the fibre cabs being able to be expanded has to do with G.Fast?

The G.fast pods that I've seen are on the left of the PCP, as most PCP expansions (for extra tie pair space) are on the right, only seen a couple on the left.

I suspect the G.fast pods could be made to affix to either side of the PCP.

They can be mounted either side as required.. there is one in Swansea town centre mounted on the right side of the pcp.

I'm not saying it's not possible but the G.Fast pod is connected to the FTTC cabinet using a twin cable which has power and fibre in it. The G.Fast pod gets its power from the FTTC cabinet and the fibre link also goes back to the other cab. So I'm not sure how it would all work if the FTTC cabinet wasn't there. It's possible of course, but I'm just not sure if BT's research ever took them down that route.

Thought as much.