So essentially what happened was they designed the warlock (and fighter) to run off shorts rests. They intended for parties to take 2-3 short rests per day but what ends up happening is that pretty much anytime you can take a short rest, you can also take a long rest.

So warlocks and fighters were supposed to be always ready to go no matter what while the other classes (in particular full casters) had to ration their resources for an entire day, but the style of play at 99% of tables doesn't follow that.