Because I spent 30 years in the cleaning machinery business & I've sold thousands of them (badged for another manufacturer).
They are a joy to demonstrate, they change the colour of many carpets, they virtually never break down even in 7 day commercial cleaning regimes and if they do they are simple to repair.
Huge top fill bag, clean vacuum turbine, bag full warning that really works, electronic brush control, brush clutch, replaceable brush strip (takes less that a minute), fantastic edge cleaning ability - the list goes on.