Here's the real truth
"We're running out of mobile suits" is code for "we're running out of shit people care about"

Which do you think more people care about
A.Gulp Shitto's custom Gelgoog that showed up in a single photo of hobby Japan issue 112 back in 2001 and the only difference is a yellow shoulder armor

Or

B. Wing fucking Zero Custom

Also did you maybe consider that the devs are just tired of only doing UC suits and want to try something new?