Yeah, they left, along with CGP Grey, a very long time ago. The TL;DR of why is: as early members of Standard, they thought that they and the other early members should be entitled to take a larger share of the income from Nebula than newer creators. Everyone else thought it should be shared more equitably. Essentially, Kurzgesagt and Grey wanted to be able to leech off of the work of others, instead of operate in a worker-owned business where everyone is paid according to the value they bring in.