My guess is that a lot of people went to https://apple.com/feedback and complained that they had to search through the alphabetical list to find the apps that used the most data, so iOS 12 puts that info at the top in order of data used. I can sympathize with that, because I have over 300 apps, and it really was a pain to have to search that list for the offender when my data usage spiked. So this change is a real benefit to me. Storage usage has always been reported in order of memory consumed, so this change brings the two into alignment.
The apps that have used no data are still listed alphabetically below the list of data using apps.
You can use the same link to ask Apple to change it back, or to make sorting an option.
I will ask, however, if an app isn't using data why do you need to look for the one you want?