We thought long and hard about what type of marketplace we wanted to create. We ultimately felt that there was a requirement to gate the marketplace on both sides to prevent bad actors from parasitizing the site (see LinkedIn). Engineers are in such high demand, that they go, inevitably recruitment agents and others will follow.
Github isn't perfect, but we our use of it is primarily as a signal of the type of people we want to attract (developers only) and as an additional admin hurdle for bad actors to have to go through.
So, yeah, we took a risk. Higher friction at the both ends (employers are curated, again to stop agents), but our aim is to create a high signal, zero noise matching service for engineers and this was the way to do it.
Our plan is to add further login options - bitbucket, stack et al. v2.
Hope that explains some thinking about the sign up flow - feel free to ping me any questions!
Hung