They do - but they also have scores of super smart engineers who each year manage to find a certain something - be it a loophole, or just something nobody else thought of.

See DAS this year, F Duct in the early 2010s, the 2009 Double Diffusers (when they were technically banned), Blown diffuser, CF layups that cause the front wing to flex under load etc. etc.

The regulations serve three main purposes which seem reasonable:

1) Increased safety

2) More entertaining racing (not much success here so far)

3) Reducing the cost so that it is economically sustainable even for smaller teams.

Still, the current cars are the fastest F1 cars ever.