Everyone has a different situation. Just because you have a mortgage, 2 kids and can afford the money doesn't mean everyone can. Some of us pay ridiculous amounts of rent by ourselves because we can't find another place to live at the moment, have a few animals to pay for food each week, and then have other expenses, like groceries, laundry, etc., to pay for. You get to split costs with a wife. Some of us pay our way alone. It's not that I personally wouldn't want to help a site I go to, but, there are other things I need the money for. It may seem like small change to some people, but, it's another X amount of dollars I could use for a mini emergency, something I may really need, dinner for tonight, etc. Also, some people don't want to spend money on a site that they may not be in a year or two down the road (not saying that is me, I will probably stick around for a long while).
You can't judge everyone based on your own living situation. That's cool that you can put aside a bit of money for a website, but, not everyone feels that it's the best place their money can go.