Why did grey squirrels out compete red squirrels in the UK?

Thanks for your help.Why did grey squirrels out compete red squirrels in the UK?
Grey squirrels are big, mean, and generalist, and not shy. A red squirrel is easily bullied out of prime territory by the aggressive grey squirrels. In addition, grey squirrels do extremely well in urban habitats because they eat anything and do not fear humans. Red squirrels are considerably more shy and require more forested habitat.Why did grey squirrels out compete red squirrels in the UK?
They're somewhat bigger but, more importantly, they're much less fussy when it comes to food. That allows them to flood the forest with offspring. Essentially, in most of Britain, their success was due to their rapid increase in numbers. It was more a case of eating the reds out of the game rather than beating them.