Because Google Chrome on iOS pops up asking to remember a password
Safari on iOS suggests a password even if I'm trying to paste on in from my password manager
OSX can be the same way
They all sync
and I never bothered to disable them because I never thought about it, but sometimes I'm in a rush with a service I think I'll never use again and use the suggested solution in one of the browsers
Unfortunately, and I hate to "victim blame" (though you say you are not yet a victim), I think you have to take some responsibility and use a password manager with deliberation. IMHO the browsers all make this worse by giving you something that seems to work and your first notice that it doesn't anymore is when it stops, which is a terrible way for a security feature to work, but obviously they have incentives to lock you in, and boy oh boy is this one of the biggest ways that a browser can lock you in.
I think you should resist sooner rather than later and switch to something cross-browser and third-party.
Safari on iOS suggests a password even if I'm trying to paste on in from my password manager
OSX can be the same way
They all sync
and I never bothered to disable them because I never thought about it, but sometimes I'm in a rush with a service I think I'll never use again and use the suggested solution in one of the browsers