I don't know how this is with iPhones (I don't own one), but with Android these events are almost 100% correlated for many people. That's because you never get prompted for your Google account password on your phone. If you don't use the same Google account on your phone as on your desktop, or don't really use your Google account on the desktop that much to begin with (both apply to me and plenty of others I'm sure) then you might never need to know your password. I've seen people not even realise that they have a Google account, despite using one every day on their phone. Is there anything significantly different with Apple accounts?
In case it seems unlikely that someone would not use their phone account on their desktop, remember that plenty of young people today don't even have a non-phone device.