Wellllllllllllllllllll Stu.. the simple answer is.... we LIKE looking silly... we ARE supposed to be eccentric ya know!! We also love history and tradition.. silly as it may be.. we love it. .. and why not :)
They are not "attorneys" in UK courts, but "barristers" and "judges"; and it is traditional uniform. However it would be a pity to lose it just because a few people think them silly; and it may enhance the point that British law developed and evolved from roots established, tested, modified as necessary, over many centuries.
As HarryDemon says though, if the witnesses include young children they tend to remove their wigs to be less intimidating.