My understanding is that they had the D4 model ready to go, but the producers rejected it (something about windows) and they decreed the D7 be used instead. Since producers come above art department in the grand scheme of things, that makes it a deliberate choice not a mistake.Technically, the D7 in Enterprise was not suppose to happen. It was a "we just don't have time to do this anymore, what do we have on hand" moment. They had a model (what Axanar is using as the D4) made for Enterprise, but it was rejected for reasons and there wasn't time to fix it before the episode went out. So the D7 was used that one time. It didn't show up again in Enterprise, replaced with the D5.
Again though, I'm not fussed with Axanar ignoring it or tweaking continuity for their film.