[forty]

here is my guess:

One thing you need to understand is that when you start generating your passwords and not knowing them, you need to have your password manager everywhere or else your are stuck. And it turns out many people use browsers and OSs from different makers. So for example keychain might be fine if you have everything Apple, but if your work computer is a Windows one, then it doesn't work anymore. And I'm pretty sure apple is not going to make a keychain for windows any time soon, just like Mozilla isn't doing Firefox sync for chrome and safari.

(I work for a company that makes a password manager)