From the complaint: the application that Vogt himself submitted to Y Combinator described repeatedly that Guillory was a founder of Cruise Automation and state

From the complaint: the application that Vogt himself submitted to Y Combinator described repeatedly that Guillory was a founder of Cruise Automation and states unequivocally in response to a question asking “who are the shareholders and what percent does each own?” that “Cruise Automation is a Delaware C Corporation created in September 2013. 50/50 split between Kyle and Jeremy." If true, that could be worth hundreds of millions, which is an even larger amount of money to walk away from.