People stayed even with the stock was getting crapped on by Wall Street, he was clearly able to convince everyone that the company would succeed and opinions of the companies future would turn around.
Going to Tesla a few years ago was a hard choice, they paid below market (substantially) but offered pretty generous stock grants.
The stock hadn't really appreciated in-line with the companies growth because of the enormous risk of the Model 3 project. This represented massive risk overhang that until cleared didn't allow the stock to really take off.
2020 (over?) corrected for that however so now the employees that have put in the years are sitting on massive unrealized gains.