Have you ever watched any Shaco video EVER? Chances are that you didn't.
Now i don't have the time to go in-dept, nor do i want to, but i'll explain the basics to you.
Shaco's boxes are made for 5 things
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To delay the enemies (includes delaying enemies near objectives to secure them)
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To damage enemies (read right above)
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To secure an escape route
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To survive ganks/win fights
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To use as CC in teamfights (tactical retreat tactic)
Now any good Shaco player will not just place boxes randomly, he will choose and position his boxes where enemies might go through in the near future, he will plan a minute of the game ahaid everytime he places a box.
Now for example: Say you're laning blue side bot lane as Shaco support, you place a box in the lane bush, since the enemy support might engage you, you place a box near the river walls, so that the adc dont have to worry about being jumped on by the enemy adc, and since you know that the enemy jungler is near his blue buff, you place a box behind you, to make sure.
Now, if that box behind you, in the end, serves no purpose and just disapears after a minute without it having been proc'd by anyone, it doesn't mean that it was ''place and forgotten'', it means that the gank didn't happen, but COULD have happened, and that the box would have most likely saved your adc's butt.
Do you understand so far? There might be Shaco players who just place boxes randomly everytime they're on cooldown, but it just means that he's unexperienced/just doesn't plan ahaid.
Alot of times when i invade the enemy jungle (even when i'm laning) i'll place 1-2 boxes in the nearby area so that i don't be disturbed when i take that blue buff, sometimes they don't get proc'd, and 50s later, some low hp enemy will run there and die while you're away. Now THAT would be considered as ''place and forget'' because it was a random encounter, yet the SAME THING could happen with Jhin's traps, i don't know why you're trying to say that Shaco's boxes are the only invisible traps with which that could happen, but they're not.
I take time to place my boxes in strategic positions every fight, anywhere i go.
And as for Jhin's traps taking ''skill'', nah, they don't, you don't have to be a genius in order to hit your snare on them, only a little bit of map awareness and memory.