Simply because he did not need to. Above the cloud, hole over Vauxhall, descend through the cloud with enough speed to keep at the peek of the power curve (minimum power). That is much safer than hovering down, which has risks such as entering vortex ring state (at low level you might not get out of that before running out of height).
PB had no problem with the flight - that I can discern from the facts we have so far and from what I know - until he was below the lower cloud layer, and making the final turn.