Maybe there's an internal policy at which $199,999 is a cut-off, i.e. at a certain point, the sponsorship decision is moved to a higher-level of bureaucracy and approval. Which is completely the sensible thing to do: there's no reason why President Obama has to be the one who personally signs off on million-dollar toilets in Iraq (even if the buck stops with the President), and neither should
every sponsorship decision be put on the desk of Mark Zuckerberg or Sheryl Sandberg...and an efficient way to do that is to set off a discrete cut-offs, so that you don't have a middle manager thinking they have the discretion to do the exact same moral reasoning as you suggest,
"Oh why just give the Palo Alto Elementary Science Fair $10,000 when we could give it $100,000 and no one would even notice?"Besides internal order, I imagine there's additional concerns and contractual obligations that relate to a public company's stakeholders, e.g. the shareholders who invest with a guarantee that a company has consistent policies in place to manage its spending, whether operational or charitable.