Advertising on the internet is paid for per click. When you click an ad, the advertiser pays (often indirectly) the site the ad was on some amount of money. For a lot of Google ads, that’s 50¢ or more. I’ve seen some ads go for as much as $2.
So, if you’re reading something respectable, and see a worthless ad, click it. Cost the advertiser a half coin or so, and make a donation to a site you like to read in the process, all at no cost to you.