all the companies that would have sold the jet fuel to Google at a profit did. The government acted in competition with private enterprise to fuel private enterprise aircraft.
You're ignoring the fact that extra jet fuel was simply available at a discount, because NASA had already bought it. What should NASA have done with that extra jet fuel? Sold it to a private jet-fuel company? Let's say that they did that. They would have had to sell it at a discount (maybe the same discount) because the jet fuel was located at an otherwise-unused airfield and would have to be transported elsewhere, which is not free.
Oh, you say, they could have sold it to the same private jet-fuel company that Google has contracted to fuel its planes! That way no one has to transport it - it's already in the perfect location! Knowing this, NASA should definitely ask for more money for the same jet fuel, because NASA has basically already paid the cost to transport and store the jet fuel exactly where the jet-fuel company needs it. Jet fuel company buys that fuel and sells it to Google at market rate (since Google would otherwise just buy different jet fuel from one of jet-fuel company's competitors.) I don't see how the private jet-fuel company would make any more money than normal. They saved on transport/storage cost but had to pay that savings for the fuel (because NASA knew they were saving). That is, unless you expect NASA to give the jet-fuel company the same sweetheart deal on the jet fuel that it gave Google. And if NASA did that, then it would be giving a private company a taxpayer-subsidized advantage, the very thing you were just complaining about.
NASA was not continuing to buy jet fuel at its government-discounted rate for the sole purpose of fueling Google's planes - the fuel already existed, and the question was what to do with it. NASA either gives someone a deal on it and someone gets a taxpayer subsidy, or doesn't give anyone a deal and all private-company costs and profits are identical to what they would be if NASA's fuel wasn't there at all. NASA comes out ahead in the latter scenario, but that's not what you complained about.