Well it's more than that though too. In England because it's a wet and moderate climate the pitches don't tend to go hard and bouncy, and don't usually take much spin either. So if you've got a pitch that probably won't spin and probably won't be fast and bouncy, what else can you do? Either yuo prepare a pitch like the two against Sri Lanka and the one at Trent Bridge which produce terrible boring cricket, or you can leave grass on the pitch and hope it'll help the seamers. In fact, the Lord's Test vs Sri Lanka was also a pretty green pitch by normal standards and that was a dull flat wicket in the end, so really the pitch we have today is about the only option if you want to cause exciting cricket.