But that's a fallacy, really. Even the best procedural generation can never reach the quality of merely competent hand-made design. So instead of levels that are infinitely replayable, you get levels that aren't fun even on the first playthrough.
I agree that is the case in many, probably even most procedurally generated levels.
Certainly not in all, though. Diablo (all of them) comes to mind, Minecraft, Civilization, WBC (yes, they are imbalanced there, but screw balancing, seriously), some Wizardry/EotB-style games have that, roguelikes, many survival games, etc. etc.
Also, this "Even the best procedural generation can never reach the quality of merely competent hand-made design." reminds me of the people claiming that man will never reach the skies/stars.
Oh, ye of little faith!
Give it some time, let the hardware grow so that generation algorithms can create truly wondrous levels in little enough time. So that the generation scripts can actually be an AI behaving like a level designer - instead of some pretty simple scripts like most currently are. Or let the level designer not design the level but fine-tune the algorithm.
All of this is already possible, but would probably still require LOTS of time to create a full world with at runtime.
I also forgot one important point:
Many developers simply hate level design. I know I do. Trust me, I tried. It's cumbersome, takes a shitload of time for very little progress. Modern engines help, but still... Ugh!