I don't want to have to make accounts on websites just for them to remember what is in my cart for my next visit. I don't like having more accounts, especially if I'm not yet sure if I'm going to buy from them.
Since the site does not know you are leaving, it doesn't have any opportunity to prompt you and ask whether you would like to save your cart (and if it did I would find it pretty annoying)
If I go to an e-commerce website and I am not signed in to, add a bunch of stuff to my cart and leave, I have absolutely no expectation the cart will persist until the next day, and I really don’t think you should either. Not only is it in an unreasonable expectation as an end user, but also it sounds like an absolute nightmare for businesses (Do you hold physical inventory for things in the cart? What about price changes or products are discontinued? Etc).
In practice, sellers do deal with this. The most common approach is that putting something in the cart does not reserve it or maintain a fixed price. Then if availability or pricing changes, they flag that to the user when viewing the cart.
Also, you initially asserted that the regulations were strict for any and all cookie usage. The person replying to you provided plenty of evidence to the contrary, and now you’re bringing up incredibly niche edge cases, to what end I’m not sure. I think it would be more productive to just concede that the regulations aren’t as strict as you stated.
Most companies will not be compliant unless they do one of (a) get consent from users or (b) hire a lawyer to review each of the things they do in the context of ePrivacy, and make corresponding changes to keep everything within the bounds of "strictly necessary". I'm bringing up these 'edge cases' as part of showing that most sites would have changes they would need to make if they wanted to stop asking for consent from users, and that these changes are not obvious and go beyond removing tracking.
Since the site does not know you are leaving, it doesn't have any opportunity to prompt you and ask whether you would like to save your cart (and if it did I would find it pretty annoying)