It's a little different if the volunteering is something low impact or something you're way out of your depth in, or if the cause wanting money has a way of getting very tangible rewards (which are quantifiably greater than whatever free time you can spare on it)
And this is for congressional-level. For state senate, state house, local gov, etc. I imagine this could go even further. City councils and mayors have lots of impact but little donations.
10k is not a lot at the presidential election sure, and maybe not for Senate either, but it is a lot of money even in House races. And for many state races.