Having your passwords quickly available on every computer, every phone, every OS, and every browser is great. Browser-plugin + app password managers do all 4, while password managers provided by the OS or browser typically fail at one of those. They fail hard, too, by making it difficult to manually extract passwords when you need to. They also tend to lack features like password generation, note storage, etc. It's a completely different experience, really.
And — at least on iOS — is glacially slow. Startup times of twenty seconds weren't the rule, but not uncommon, when I tried Lockwise last week. Even at the best of times startup took five seconds at least.
Not the parent, but for my own use case, I use password managers for things outside of the browser (office door code, steam, this kind of thing). It might be possible to enter those in the password manager of the browser, I never actually checked, but in any case that's why I use an out of browser password manager
One type of incident I came across repeatedly was the browser would not recognize new password setup after password reset. Also found that 2fa systems were being confused for new password accounts.
I agree password managers like last pass fill this void quite nicely. But are not serviced to run on mobile without payment.
