You can call AppleCare and have your Apple ID deleted any time you want.

you actually don't believe that they delete your data, do you?

Not sure why you are being downvoted, but as someone who did try deleting an appleid, there is no self service way of doing so. Basically ended up removing all possible data; and filling the rest with fake values. Finally I changed the password to some random string. Not sure how much aux/opaque data remains that I could not see (eg location services), but this was secondary throwaway account, so I didnt care much.

This must be one of those "alternative facts" I keep hearing about.

I literally just now created, and then deleted, an Apple Id. It's trivial. Why do you think it isn't?

The fines are indeed substantial: up to 4% of annual turnover. On top of thay they can force you to shut down the service in question until remediated. For an e-commerce company that can be even worse than the 4%.

Being fully compliant with GDPR is a mountain of work even if you thought you were doing all the right things before.

In practice, small companies/ start-ups might not be audited / reported / pursued very much but: a) you'll never know and b) at least all the big tech and e-commerce companies are smack on in the sights of several data protection and competition(!) authorities already. We're all scrambling to be compliant in time.

Source: first hand account from running the GDPR compliance project in e-commerce company.