It's nothing to do with being 'even all over'. It's to do with the plastic grass and underlying surface producing more friction against the boot. Plus, it's one thing having a kick about for an hour once a week, but plenty of managers have complained that playing and training on an artificial surface leads to problems like back injuries. It is just possible that the people that make their living from playing the game no a wee bit more than the punters that enjoy an occasional kickabout.
And if they were that great, why aren't we seeing them across world football? They are rarely used even here in the US - home of everything plastic.