I get what you are saying, but I think something is being missed.
Let's take a single third round pick. I agree that holding onto a 3rd rounder just because a draft year in the past a third rounder was a home run, is foolish thinking, and the statistics of the return for that pick back it up.
The thing is the pick not only has value for cheap talent. It also has value for trades.
For example, if you have an extra 2nd round pick, a GM could flip a first and 2 seconds for a player they need.
If they don't have the extra second, or even worse lack any second rounds picks, then they either need to add a prospect and or future picks, or eat salary, etc. etc.
Furthermore, if you trade several picks for a player, and they don't pan out, then losing the picks was not only bad because "we could have picked X, Y, and Z" with those picks, but also because we now don't have those extra picks to trade for what we need in the future.
I mean there are only so many things teams can legally trade to acquire talent, so being frivolous with draft picks can be poor asset management not just because we missed out on one third rounder who became a great player or whatever.
Note: this is a big reason the Eric Staal trade was such a stinker even though it was "only 2 second rounders"