CSL+ University of Toronto v UCB ACE

because it's much easier to kill one cannon than one pylon

But then, it was multiple cannons and one pylon. One pylon would have left the many cannons useless.

I used to think the same way but it's usually not worth it. pylons are 300/300 so it takes 3x as long to take down with 2 cannons attacking. Attacking the cannons meant 2 cannons attacking for 1/3 of the time then 1 cannon at a time after that, the others barely even got a shot off before they went up.

Also, attacking the pylon gives the lots more time to attack. With cannons they can run in attack and run out before the lots get many hits

Also, once he sees his pylon being targeted he can build another pylon further behind his cannons and have all his cannons up again pretty soon.