Even when the old ways were allowed to work
, there was no simultaneous movement of flaps and L/G during the GA sequence. By the time pilot's hand touches the gear lever, the flaps would be well reconfigured.
Personally, I like the explanation already provided above, expanded. During approach, F2 take about 5 sec to extend against the airflow, powered by G & Y pressure delivered from one EDP in the OEI scenario. Simultanoues demand of the LG operation at that stage will cause hydraulic pressure drop below the ECAM warning level, causing nuisance warnings and god knows what other side effects in the F/CTL system. The demand is quite substantial, e.g. during normal take-off the PTU runs momentarily in support of the G HYD anyways.
To avoid the uncecessary, there used to be a note in the SOP so that the drill of extrending the flaps and gear could remain the same after an engine has given up. Exactly the way it shall be done, a good SOP set already caters for single failures.
Maybe the suggestion got removed in pursuit of operational benefits you speak of, whilst knowing no harm would be done - a simple change of heart?