Money is important, obviously, but it's not always the only thing that motivates people.
The median software engineer salary in the US is something on the order of $120k/yr. The GS pay scale tops out at just under $160k before locality is taken into account and that's only a small single-digit percentage increase at best, but nobody is getting hired as a GS15 to do development work.
You will make more in the private sector for sure but "hundreds of thousands" is going to be the minority by far.
Edit: After a bit more research there's a separate executive pay schedule (not that different than the private sector after all) but it's not super clear to this outsider what determines which schedule you get on other than probably just defaulting to GS.
Also 18F has special hiring authorities with 2 year appointments that are not restricted to the GS pay scales for the very issues you bring up.
> https://join.tts.gsa.gov/compensation-and-benefits/
That is the page where you find jobs for 18F, nothing there indicates anyone at 18F is not on the GS scale.
It's important to note that that is GS15, step 10, with the maximum locality adjustment (which I think is just Alaska but California is not far behind). GS15 step 1 is going to be $123k before any locality adjustment so still very likely under $150k/yr unless you're in one of the highest cost areas. Alaska is 32%; most midwest states are 17%.