Again it appears as though the innate language faculty is at work. Other sorts of drift seem to be slow and highly constrained, such as vowel drift in American English. I haven't studied much phonology, but it seems that as two vowel sounds change, the changes in the other vowels is predictable. In any case, the point is that these changes are not random but regular, so something must be constraining them. Inventing implies a deliberate act by some agent.
Etymologists can often pinpoint the origin of a word or phrase with surprising accuracy.
But the changes which occurred between Middle English and modern English, for instance, or even those between British English and American English, are much more gradual, and can rarely be attributed to a single area or event, let alone a particular person.