Conceptually, it’s not an unreasonable way to balance things that have the capacity to hit large numbers of enemies. The caps that were selected though… some were truly bizarre.
I’d be more interested in why they gave some low-cleave weapons no limit on the number of targets they could damage 
The answer is probably “Brutal Momentum”, but that didn’t hold true for things like the Power Maul or Slab Shield (which lacked the target cap to do anything useful with BM)
Fatshark being Fatshark, I guess!
That’s interesting, that a non-damaging hit (from a critical strike) counts towards Invocation of Death 
I’d asked about that in the past - while the in-game description has separate Cleave Distribution values for damage, the devs chose to scrap it and use a singular value for both. I’ll see if I can dig up the thread.
EDIT: This bug report thread is where one of the devs added some explanation - Crucis Mk II Thunder Hammer Cannot Cleave
The breakpoint calculator is a far simpler way to see the figures*, but it’s all available in the lua source
For example, the Eviscerator; each section (beginning with { and closing with }) represents the weapon’s properties versus the Nth target in a hit; first 4 sections have a non-zero value in the attack fields, then it drops to 0 and subsequentlly no_damage (I don’t know what the difference between 0 and no_damage is)
*The breakpoint calculator doesn’t show cleave damage for sticky chain weapon attacks. I don’t know if there’s a specific reason for that; it’s probably for simplicity more than anything, since the rip/saw damage can happen on any target (depending on your cleave)