Several things come to mind, one is that all humans are selfish, some just much more so than others. So we form our own base lines and judge from that, and every one is better that their base line.
another thing is $50 a year is much, much less than I normally give to pro 2A organizations in a year, I suspect that’s true for most here.
We cannot ignore the very real disconnect that there are from 40-80 million (perhaps more, we'll never know) gun owners in the US, but only about 4-8 million are motivated to be active in gun rights organizations.
This is another thing and it’s highly unlikely to change. Most gun owners are casual (for lack of a better word) gun owners and that’s not going to change, they just don’t care enough to be donating money.
For example, I smoke cigars, fine, hand rolled, premium cigars. While not as public, big brother is an enemy of the entire tobacco industry. I probably should give some money to the cigar industry advocates, yes a few exist. But honestly I don’t care THAT much.
Same thing is true with old muscle cars, some people want them only as museum pieces because they’re such polluters, not only can I not care about everything, I also can’t finance everything.
And the last thing that comes to mind, is your really making a moral argument, which is basically
We wold be better off we’d take a $50 and send to fight for gun rights rather than buy a box of ammo.... well according to The Food and Agriculture Organization of the United Nations approximately 8,500 children die everyday from “improper nutrition” (AKA starvation/malnutrition) so one could argue.... well you see how this could go on forever.