The core statement that the issue is with is:
"But ability scores for monsters meant it became way too hard for DMs to create their own monsters, and creativity is something D&D does better than any computer game."
Ability scores were general, free-form measures to encapsulate a variety of stuff. If the issue is simplicity, the question would be why D&D3 includes so many stats for monsters (touch AC, flat-footed AC, regular AC, Base Attack Bonus, attack bonuses with different attacks if the monster has feats that mod those, Fortitude save, Reflex save, Will save, Hit Die type, Hit Dice, hit points, etc.) that follow very rigid rules with different progressions for different monster types! Ironically, out of all these numbers, the only ones GMs were allowed to set, at personal whim, were the attributes.
If the issue is compliance -- that is, if GMs felt they had creative ideas, but because they couldn't navigate the number system to "correctly" build them ... well, either the game is too complex at its root, or a GM could just invoke the most basic rule and simply ignore them. (Double check the math in many Origins-Awards winning adventures.)
Eliminating generic attributes for monsters ... while miring monsters in dozens of combat stats, sets a formalized precedent that "all you do to these monsters is hit them until they run out of HP -- do not try general activities with these monsters, such things are too hard to conceive." Computer games are already better at making mobile entities that one hits until they die. Let's be creative!