Originally Posted by Vuther
Because critting does more damage and doesn't put you in a weird pseudo-fighter-support build with a conglomerate of effects and stats that your champion cannot simply fully synergize with while still costing a ton of cash like getting normal AD.
And unfortunately, the likes of Kog'Maw as you mentioned needs to do a lot of damage because that is what your team needs you for.
You are a very confused person. Crit is important for the majority of ad carries, but there are 4 potential effective on-hit carries in the game, plus Varus who can lean towards AD for his poke or AP for his burst, and WW who just makes madred's feel awesome. Then there are the FUN builds like Lulu, Oriana, TF, MF, and the full-on troll builds like Cho, Fiora, Renekton, Shen, or Voli.
Sticking to the serious competitive on-hits, they have the benefit of mixed damage making it hard to defend against them, which is where the bloodrazor comes in to prevent even health from being an obvious defense. This provides a great choice in any defensive meta, and the item itself would be amazing in today's health-based games. On normal carries, pure AD crit is just as effective now thanks to the lack of armor.
But you seem to need it worded as simply as possible for you.
Crit makes AD strong.
On-hit is a different damage type than AD
Bloodrazor was the core item for on-hit carries.
My on-hit Kog out-damaged both crit and AP enemy Kogs all the time, while being able to survive a rogue bruiser or assassin breaking through our front lines while they got focused.
Your argument is the same as saying lich bane is worthless on Ez because IE has crit and does more damage. It's a different build entirely and you should not confuse the two.