1) Much less, if any, grant writing. A standard NSF $500K 3 year grant provides a lab about $100K per year (due to university overhead). This will support 1-2 PhD students on a pittance of a stipend.
2) Less teaching (1 course once a year)
3) Computing resources that are far greater than you could get a grant for. One NVIDIA DGX-1 is about $100K. Very hard to get a grant for something like that. Companies have far greater resources than just one DGX-1
4) Access to software engineering personnel to help with research
5) Access to data, and the ability to create new datasets. Many datasets cost over $100K to make (e.g., those for semantic segmentation). Very hard to get a grant to make a dataset (I've tried)
6) Much better media relations to popularize your research
7) Bigger salary
A big part of this, in my opinion, is just that FB funds their labs. Getting government funding for a lab is difficult and frustrating and must be done continually, especially for these professors that run huge labs. NSF has a 7-15% success rate, and it can take a lot of effort to write a decent proposal. Including teaching regularly, this takes a lot of time from actual research. What these professors, I think, are negotiating is only teaching one semester a year and having a spigot of cash to fund their labs. They also gain access to massive amounts of data and computing resources.
Other companies don't seem to be as open to this arrangement as FB, but it has a lot of appeal to me (although I'm not a lover of FB).