Random Eddie Stobart Question?

[RossiT]

Bit of a random question I know but having spent the past 3 days driving throughout England and Scotland, my daughter was collecting the truck names to pass the time, I noticed that within the Stobart fleet they have a few Volvo's and just the one MAN we saw, what's the reason behind this when almost every Stobart truck you see is a Scania? Surely having all the trucks the same makes more sense? It can't be an age thing as I'm pretty sure they get changed every 2-3 years?
Thanks