Heathrow T5 has satellite terminals requiring a transit. Gatwick does not.
BA had terrible punctuality pre T5, Easyjet does not
BA at LHR had a high number of people travelling long haul with checked in luggage - which needs to be offloaded causing further delay. Easyjet flies only short/medium haul and has a large number of people without luggage who could run from security to a gate (or would like to try) given a chance.
I don't like Heathrow's policy. Easyjet are being too blunt in their application of the policy - at the very least make an allowance for times when a flight is delayed and a passenger can reasonably make it to the gate for when the gate will actually close rather than when it was meant to close.