I've put some links below that might explain it a bit better than I did. My info above is a mix of from google's docs as well as experience, talking to others in the industry etc.
Ad Rank[0] - this is the algorithm that determines essentially how much you pay like I mentioned. It's far more complex than my simplified explanation as it also takes into account context around the user. The device they're on, their previous searches etc. So a user who is on their 5th search for shoes and is now searching from their desktop may be more interested in a product page than an article since google may assume they're ready to buy now and they always buy from their desktop etc.
Ad Rank thresholds[1] - This is the friendly term for the reserve price I mentioned. It's the reserve price for a keyword based on all your inputs. Can go up and down depending on how relevant google thinks your stuff is at that moment for the user but generally google will set a floor for it.
Just more info[2] - more info from Google about how this stuff is worked out and what it means in practice.
If you google around "ad rank effect on cpc" you'll get more relevant stuff if you're interested.
[0] https://support.google.com/google-ads/answer/1752122?hl=en-G...
[1] https://support.google.com/google-ads/answer/7634668
[2] https://support.google.com/google-ads/answer/1722122
When you think about what google is trying to do with ads it does make sense. If they let anyone serve rubbish for any search, people will stop clicking ads and advertisers will stop using it. Google loses out.
It's in the users (arguably, depending on how you view ads), the advertisers and Google's best interest to incentivise advertisers to make their stuff relevant and good.