I don't understand why more companies don't do contextual ads, yeah. Why track users all around the web when you can go to a website about cars and put in car ads, or a website about music and sell concert tickets or etc? You already know everyone on that website is interested in the topic, and the analytics would be much cheaper this way.

They absolutely do. Every sponsorship you see on a podcast or a youtube video or a streamer is a contextual ad. Many open source sponsorships are actually a form of marketing. You could argue that search ads are pretty contextual although there's more at work there. Every ad in a physical magazine is a contextual ad. Physical billboards take into account a lot of geographical context: the ads you see driving in LA are very different than the ones you see in the Bay Area. Ads on platforms like Amazon, HomeDepot, etc. are highly contextual and based on search terms.