Let's say that just for the sake of making a point that four 2nds = a top-20 protected 1st. From there, let's translate that to currency where a 2nd round pick is a quarter and the aforementioned 1st-rounders is a dollar. One player is on the market and can be had for 25 cents, another can be had for 40 cents. With three seconds you can get those players, but if you are short seconds, you are basically faced with dipping into assets that would result in overpaying, coming up with something convoluted that nobody is interested in dealing with, or just generally not getting the deal done.
Then there's another scenario where 2nds can push a bigger deal over the top. The Jazz actually did exactly this in the Conley deal.
No one can say that 2nds aren't worth anything and then watch them get exchanged in consequential deals all the ****ing time.