a) It seemed like they were stronger CBs than we might normally be used to in the UK. Severe turbulence reported with aircraft unable to maintain level flight. Plus it was a busy day in the London TMA, possibly with some knock on effect from the previous day's distruption caused by Gatwick runway closures.
b) it could be the ramp was full or there was no handling available or some other reason but generally it's down to not having enough resources one way or another,