If Miliana wanted fame, she could have spread word before Matisa arrived, instead they stayed under the radar to keep Daites safe. Now that Daites has Matisa and Kocis, they're stronger in a military sense and can withstand the threat of invasion to control her inventions better, so they can afford opening up more. Still, it's smarter to use Matisa as the frontman. His rep as the war god is a deterrent to other domains, and he's also better equipped against assassination attempts than Miliana. As the brain of Daites, it's better for Miliana to stay hidden, safe to plot more stuff and expand her BL empire.