Juxtaposer
Outro: Divina Comedia
Didn't stop the Phil Kessel trade (pushed back to next season if they miss the playoffs, turns into a 2nd that season if they miss again).
You're acting as if your condition is set in stone, when I wouldn't even call if "often". Quickly looking over trades, conditional 1sts were negotiated twice in the last 6 seasons. 1 with your considerations (Schenn) and one with something similar to what LZ was going for (Kessel).
Are you sure there were only two conditional 1sts traded in the past 6 seasons? Where are you getting your info, because I distinctly remember Thomas Vanek being traded for a conditional 1st in 2014. The Isles ended up with a top-5 pick (Dal Colle) and so the 1st was pushed to 2015 with no conditions. Luckily the Isles made the playoffs that year, but that’s sort of the scenario that I’m thinking of.
The Kessel trade is not exactly what I would consider to be a shining example of your point. The Leafs got a really, really poor return for him.