He had leverage. Facebook's massive growth meant that he could command the terms of the investment, and he ensured that he would always continue to control the board even as he was being diluted with later rounds.
https://www.vox.com/technology/2018/11/19/18099011/mark-zuck...
This was made popular by Larry and Sergey in 2012: https://www.sec.gov/Archives/edgar/data/1288776/000119312512...
It’s really only possible if the company/investment is so compelling that investors will invest with virtually no control.