OldLurker,
the crew selected gear up …
Historically GAs have been trained as requiring urgent action. Way back in the distant past a critical issue was obstacle clearance for the GA flight path with engine failure. Nowadays with power excess, improved engine reliability, this is not a significant concern, indeed the regulators are focusing on all aircraft having automated reduced thrust for a GA (yet still require on pilots to select higher when required - but how might they know, I digress).
The aerodynamics of a GA are no different than for landing, except with added thrust you reach a point when the aircraft will not land; add more thrust it begins to climb. This is like a takeoff, retract flaps to improve ‘takeoff’ performance, retract the gear in the same way as for take off, no rush, minimise the opportunity for mistakes, …
The problem is founded in history, it is exacerbated by todays lack of joined up thinking between certification requirement, training regulations, safety management, and human factors; regulatory authorities cover all of these areas, but are they in ‘ivory towers’ (without windows).