To put it lightly, Quiet overstayed its welcome, she literally is Flavor of the Month, just like Lady D, interests wanes fast. It's been several years of Quiet and other artists have released animations staring different and new characters, and in that span of time Animo went from Patreon to Subscribestar as well. From when Quiet was introduced via MGSV to now, a highschool Freshman became a college Freshman. When other artists have polls in which character to use for the next animation, Quiet no longer shows up for those polls and hasn't for some time. Sure the anticipation of the OC interrogator getting HORSED™ but remember in the span of the years for Breaking the Quiet you could have had Tifa X Horse, 2B X Horse, Ellie(legal) X Horse, Ciri X Horse...sometimes fans have trash tastes; props to Animo taking it to completion though.
EDIT: Added more to spruce up my argument and add perspective.