It might help to think of DNA like the alphabet. The alphabet is capable of creating every sentence that's ever been written as well as every sentence that ever will be written. But that doesn't mean the alphabet somehow has all sentences pre-encoded in it or that the scribes copying the Bible were somehow wasting energy because they were copying letters, words, even phrases that later writers would also use.
That makes some sense.
OTOH, if you randomly mutate those letters, most of the time you don’t get words. It would seem that random mutations would give you a dictionary of gibberish rather than a dictionary filled with a vocabulary of useful, varied words.
If you take all the combinations possible and compare them with all the combinations of valid words, it would seem there would be far more gibberish cranking out from random mutations. The gibberish would continue to be replicated and eventually, you would not have enough words left to build a viable creature.