Named streets, to the best of my understanding as well, do not operate on a system of naming. Numbered streets make it simpler to develop a system in which navigating in an unfamiliar location will be easier. For example, going South will make the South numbers go up and the North numbers go down with the only named streets being main, center, middle, or otherwise.
Named streets do not have much rhyme or reason to which ones will be after them. Most that I know are not alphabetical, nor are they in any recognizable pattern to determine which direction I'm going. With numbered streets, I can navigate with only needing to know my directions and keeping track of what the signs are saying. I.E. I don't need to know directions, I just need to know the address.