I think I'm allowed to wonder why Rodis and Carson started with these retro style study models of Excelsior
(which look quite archaic to me) which obviously needed significant upgrades and improvements before these could qualify as late 23rd Century designs.
Unless we have a straight answer to "Why?" there can't be possibly anything wrong to speculate on the matter, IMO.
This was not pre-production work for Star Wars
(where they first had to figure out what style they wanted to have to begin with) but for the third Star Trek film, and design aesthetics had already been established by the refit Enterprise
and the Reliant
. YMDV, obviously.