"ox" stands for "org-export-". This is so to limit file name size. Some
systems are very limited (e.g. MS-DOS).
Is that file name size that important in today's time? I'd be surprised if anyone using Org is using MS-DOS. But regardless, the "ox-" prefix definitely looks better than "org-export-".
Variables and functions should really be "org-export-html..." but that
would be very long. The "org" prefix is mandatory for Org variables and
functions. "ox" would be misleading.
Does this have to do with org-export--generate-copy-script (as discussed here[1])? Is the prefix requirement for "org-" more widespread than that?