it’s a dark pattern deliberately chosen to let people get annoyed and pay for icloud. On windows people instead will accidentally fill their onedrive account and that’s it. They won’t even know that they’re using it. It might send some scary emails like “your cloud backup is full!!!11 you gonna lose everything!!111” but those go directly in spam. Error messages in windows for regular users appear like “����� �������� �����������” - their eyes don’t have the right encoding to understand the message, so they just click OK and dismiss it. Instead, the red dot is prominent in the home screen of every iphone and bother also those that don’t read the error messages…
For me it was annoying enough to switch to android. I really felt like I had to use iCloud, forced through my throat. I have ocd and a red dot means “I need to open this app immediately RIGHT NOW to clear it” - and then your can’t clear it until you subscribe