NDAs are quite much the norm at virtually all companies with an investor base. It's done to reduce the chances of employees flaunting around the companies' hidden secrets.
Whenever anything is done for legal protection, most of the people are ready to go through the︀ hassle. That hassle is smaller than the one you could get during litigation. If the︁ companies didn't do NDAs, and someone would reveal the projects to outsiders, the companies would︂ need to go and sue the people, they don't want that.