Why does the AFL insist that all clubs have a alternate clash guernsey?

They need one so that poor suckers (the public) can be conned into buying "home" and "away" jumpers. That's why I love Collingwood - we have a black jumper with white stripes for home, and a white jumper with black stripes for away - HUGE difference! Funnily enough I was always able to tell the difference between teams even as a 10yo watching the Pies play North or Geelong on a muddy day at Vic Park - so why they think with the sanitised version of the game we have now that we couldn't tell them apart is a mystery!