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I think it's down to the significant difference between them. George drove a boat of a Williams for 3 seasons for him, finding one set up that works over the weekend and sticking to it is his approach.For him maybe, however George doesn't appear to be having quite the same issues...
Lewis, because, of the brilliant Mercedes that he drove would always be tweaking his setup to squeeze out as much performance as possible - but safe in the knowledge that the car was always still good enough to do well.
Right now, the Mercedes is a bit on the crap side so it's just not working.
Let's not forget that Lewis finished 3rd in the drivers standings last year, comfortably ahead of George. I don't think either of them are happy with the car, especially when you've got McLaren really showing them up right now.