Trouble is that the whole thing had been conceptualized some 5 years ago, and only entered active production 3 years ago - during which Viv, the animators and eventually the voice actors interacted with a small, but growing community that already liked Zoophobia (from which the whole concept sprung from), and the numbers only jumped 3 years ago, when the trailer dropped.
During podcast and questionaries, Viv explained that Charlie and Vaggie have been in a relationship for 5 years before the events in the pilot, which is why they appear more like friends than a couple, and they've progressed from being just friends to being partners, so there's no blushing and shyness and all that - which, of course, are also the visual cues many think about when seeing couples.
That's one of the biggest problems of the pilot - it's built atop a lore and background that has been progressively constructed over years, so, unless you kept up with that progress, there are lots of things you aren't privy too.
And that's one of the reasons why Helluva Boss worked better as a pilot - it's a spin-off of Hazbin, had a much shorter conceptualization and development time (mainly because they used the lessons learned from the Hazbin pilot to streamline the process), and is more self-contained.
It's not as ambitious as Hazbin, but it works better due to more developed routines.