Harvard is bizzaro land. I don't know what CS50s setup looks like internally, but after taking the course, and working there for a couple of decades— one full time— I think I'm pretty close.

I learned that they always have money for stuff but rarely for staff. The class seemed to have significant corporate support from Facebook and Microsoft, and probably others— both Zuck and Ballmer have given guest lectures— but I'll bet that Harvard's governance rules didn't let them hire academic staff with outside funding or something like that. They def could use it on regular staff positions— I spent years in a full-time, permanent staff position that was funded through a project partner.

The support academics in CS50 are all done by student TAs at the lowest level, or teaching fellows— grad students maybe— for lecturing or more advanced help. The staff are for things like video production, technical infrastructure, etc. There's only so many qualified students willing to do that work and no way you're getting existing faculty to do it. I'll also bet that they have rules about hiring staff to do anything resembling instructional work.

Like I said, though, I don't know what the situation is exactly but I'm pretty familiar with Harvard.