They're buying the people who actually care enough to implement it.
F.lux is a hobby of a husband and wife since 2009. No company is listed although I'm sure they have an LLC for the tax breaks, they make no money beyond recently added donations option, they have other real jobs outside of this hobby, they have no valid patents, and last... There is another open source (GPL) program called Redshift that does the exact same thing and came out in 2009.
So I'll ask again, what is there to buy?