Alphabet's various "other bets" outside of the core Google business are all pretty bold businesses. They were born of reckless curiosity, so when Alphabet hired up CFO Ruth Porat and began changing the focus of moonshots to making money, and holding projects accountable for poor performance or lack of a concrete business plan, project leads, R&D team members and the like began a mass exodus that has spanned years. While many simply felt that they had reached the limit of what their talent could do for their current role and wanted a bigger challenge, some wanted more freedom and less control from above for the sake of ensuring profitability.
Whatever his reasons may have been, the newest member of Alphabet's staff to make the jump is Dave Vos, the former head honcho of Project Wing. The aim of the project was to produce drones that could be used to deliver goods, and to help authorities navigate the creation of a relevant legal framework to allow for such drones. According to sources close to the situation, Vos' talents were enough to get the department to a state of relative stability, so he may have left out of boredom. Since drones are technically hardware, he may have also left due to control from higher-ups like Rick Osterloh, Ruth Porat, and even Google founders Sergey Brin and Larry Page, who have helped Alphabet to guide ventures toward profit since the switch. The official, typically ambiguous story is that his aim was to "pursue new opportunities".
In Vos' absence, Project Wing will continue to operate mostly autonomously, under relevant guidance from above. Vos, who was with the company for about two years, reportedly managed to get Wing to the point that the project can deliver tangible results, as evidenced by a test delivery of Chipotle burritos. While the future of the project isn't exactly set in stone, Vos did make sure to leave things on a good note. As for Vos' own future, he has not said anything at this time. According to his LinkedIn Page, he holds a Ph.D. in Aerospace Dynamics, Estimation and Controls from MIT, which means we may be seeing him in another high-level aeronautics-related position soon.