ZBrush was a 2 and 1/2D painting application. People knew of it but many thought it was interesting but not useful for day to day use. Then Pixologic explored the idea of taking the 2 and 1/2D feature set and turning it into a fully 3D sculpting program. They got several studios to help them with this through beta testing and answering questions about what they wanted in such an application. They had what seemed to be (and continues to seem to be) an unending supply of money for research and development.  When ZBrush 2 released people couldn't imagine the polycounts Pixologic claimed were truthful - nor could they see a use for so high a polycount. Fast forward to the present and there's not a single FX studio that can get by without some form of sculpting now - be it via mudbox, zbrush or another application. I was invited to beta ZBrush 2 and turned it down because I was one of those artists that couldn't see a use for all those polys (and honestly, my work in Rhino at the time wouldn't have needed it). Still kick myself everytime I think about it. lol