Using an affiliate link without disclosing it is just a scummy practice. To me, that's similar to not quoting a source. Like, come on, just put (affiliate) after the link or something.

Why does it offend you that someone makes money when you make use of the web site they created? It literally costs you nothing at all, while the site creator spent time and money making this available to you.

Because it makes it clear that there might be a wrong incentive for recommending that product.

For the same reason people on here write „Company X is better than Y for Z reasons. Disclaimer: I work for company X“

1. it puts into question their recommendations.

2. it creates an incentive to put these spam articles all over the place which creates noise.

3. they could have disclosed it and then it would have been at least transparent.

Let's say they have a financial incentive. In order to increase their revenues through affiliate links, they'll need to please their clickers. Because then the clickers will come back and click on more links, and recommend the site to their friends.

I.e. a financial incentive increases the incentive for the owner to create good links. No incentive means why should they care?

No it doesn't since clicking on a link thinking that it's a free resource and getting tricked will "taint" your amazon account for a 24 hour period. if they spam it enough and trick enough people to click on it it's not dependent on writing good "copy"