Is there any particular reason why Shaco's boxes don't proc Liandry?

[{quoted}](name=NyX Reks,realm=NA,application-id=3ErqAdtq,discussion-id=oMamzAAm,comment-id=00030000,timestamp=2016-03-06T15:47:36.764+0000)

what about plants? They proc liandrys

Yeah, you're right, her plants are also considered minion units. Unlike Shaco boxes though, for whatever reason, when designing the skill they chose to give her plants a specific/somewhat unique on hit application, similar to Ezreal Q, and I know there's other on hit abilities in the game I'm just at a loss to think up more.

This is from the league wiki directly on zyra plants:

PETS Control type Champion-influenced AI Target type Minion On-hit effects Is blocked by Counter Strike and Refuge ( Aegis Protection is not activated ) Spell effects Applies effects as ability damage; a damage over time; pet damage; and magic damage, whichever is most appropriate for the effect. Protection

Banshe's Veil item Spell shields will block an attack.
Silence icon Silencing effects will prevent plants from attacking. 

Priority

Against champions, Zyra's basic attacks apply a refreshing high-priority mark for 3 seconds and her plants apply a non-refreshing lesser-priority mark on their target for 3 seconds.

Sources of Taunt icon taunt, even if they are out of range.
High-priority marks, prioritizing the most recently applied.
Lesser-priority marks, prioritizing those nearest to the plant.
Champions within 350 units of the plant (prioritizing nearest).
Non-champions Zyra has recently attacked (prioritizing most recent).
Any unit in range (prioritizing closest). 

I realize that doesn't answer the, "but why not Shaco too," question. For that I would assume it's because AP shaco is somewhat annoying to deal with already, maybe it started out as an on hit and they changed it? Maybe it never was? I couldn't answer that to be perfectly honest.