Earlier quoted context omitted.
So when amazon suggests that you might want to buy a certain bike helmet based on the fact you're buying a bike, you find that information utterly useless?
I do find it utterly useless. If I'm buying a bike then I either already have a helmet, or already know I need to buy one. So what value is the ad providing? I'm not going to blindly purchase something without doing at least a little research (to check prices, at the very least), so the ad is just getting in the way and wasting bandwidth.
Every other homo sapiens sapiens finds it difficult to stay abreast of all the submarkets he/she participates in. They spend their mental energies on other things, or simply don't care to research products costing under some threshold.
For example, I consider myself very savvy at computer purchases. However, I really can use guidance in purchasing power tools as I'm not a frequent user. In fact, I really wouldn't be surprised to learn that of the existence of entire categories of power tools. Just because I'm not seeking them out doesn't mean I couldn't use them around the house. Oh, and I don't really want to spend a lot of time researching them because I actually do have better things to do. Also, I freely admit that I have never researched tape; the benefits of one vs. the other are a topic of which I am wholly ignorant at the moment. (Obviously you are not possessed of such an ignorance.)
For the homo sapiens sapiens other than you, sometimes a little nudge is actually mutually beneficial. An ad might make us aware of a product category, or an upgrade to an existing category that makes it more useful to us. All of these might make us do more research, or simply go buy something.