Dark Harvest - Why certains champions Can proc Dark Harvest and others can't

I have been playing with DH, for a while now, and i have realised that passive doesn't proc Dark harvest

The reason was because passive is a proc, and procs don't (proc(procs))

but then I tested this with and , I found out that there passives didn't proc DH. and don't break the rule, of procs can't proc, procs. as it's not a 3 hit activation like , just a single hit. So maybe it's just that passives can't proc, proc's. but then there's .

passive works, with every spell, and somehow procs DH, why is this? Well it turns out, that passive is classed as a spell, so that's why it works. Which to me, just sounds stupid.

I don't see the problem of other champion like darius or twitch being able to proc, DH with their passives. so why does riot only allow to proc, it with his passive but not allow others. The only reason why can go DH is because he procs it with his passive, if they allows more to proc it, more champions could go DH.

I find their reasoning to not be consistent.

If E was his passive, he will no longer be able to proc DH, with his Dot. but lucky it's his E passive so its does proc it. I wish riot would allow DH to proc with all abilities or just allow passives like and and to be able to proc it.

passive=(Bleed) no Proc passive=(Poison) no Proc passive=(Bleed)no Proc passive= (Burn) Proc E passive=(Poison) Proc