I cannot tell you how crazy this drives me. I main support and love playing tanky ones, but almost every game, the adc just ignores my attempts to grab the cannon and takes it anyway. I tell my adcs every time, but they ignore me, and it leaves me feeling like I just want to let them die to get revenge.
If you want to win games and have an awesome support, don't steal the cannons!
Cannons happen to be the fastest way to complete the 500G quest. 20+ minutes still with trinket wards if the ADC keeps denying cannons.
yeah the reason why 
is the best one in the game is because how it works
early game 
means if u accidentally last hit with an aoe ability while poking it slows your gold generation
and heaven forbid u get a terrible adc lose tower early and the enemy bots opponents roam. to help other lanes
thus making it so the only way to get to the 500 is to proc it on an enemy tower, which btw you also cant ward probably because u haven't completed it. and if u try to match a roam your mid laner will yell at you to go down bot. and stop "leeching exp"
then we have 
which again is good, except past 15 minwhen your team grouped no one will EVEY let u last hit any minions. or they will leave u in a sideline by yourself and not get in range for tribute. while u cant even clear the damn wave. ( or not follow you to begin with)
is the only one which has no drawback to gold generation at any phase.
there is no built in prevention form before u reach 500, and there is no dealing with teammates never letting you last hit that has.
