Could Apple fill up my iPhone Storage on purpose?

Some time ago I got an annoying badge notification, that my iPhone storage is full. Opening it did not show me an overview of the storage usage but an full screen ad banner for an iCloud storage plan. The badge did not go away after opening it. I deleted a bunch of data and moved on. Now a couple month later I got the same badge again without me adding significant data in the mean time. I discovered that the whole freed space had been eaten up by a mysterious "system data" again. And I got the same ad again. After reading up on this issue I made a backup and reinstalled the iPhone from it. Now all my data is there all the apps and everything works the same as before. But this procedure freed a total of 7GB "system data". Which is 20% of the whole storage of my phone. My question is: Is it normal for a modern OS to use up so much space without a noticeable benefit to the user? Or is this bad design by Apple? Or could this even be done on purpose by Apple to entice me into a Storage Plan or buying a new Device?