QUCS Studio is maintained by a single developer, Michael who was a founder of QUCS. It seems they have had disagreements about how to keep the development of QUCS itself and the project split into QUCS Studio and now QUCS-S.
Michael seems to not like open source and wants (deservingly so) some reward if he was to share the project, he suggests crowd-funding it several times in this forum. If they could reconcile QUCS Studio and QUCS-S (from Vadim and Mike) and keep it open source that would be awesome, maybe it could become KiCAD for simulation.
It doesn’t seem its a possibility for now.