Browser password management is simply not enough. For one, they just save the terrible password that the user entered (the same password they use everywhere else, incl. their bank), they don't generate one. And sure it's really easy to use with websites, but what about apps? What about computer logins? What if the website changed their login domain? What if they changed to a 2-step form and it doesn't autofill anymore? What if you tried to change your password and the browser updated but the website didn't? (Hint: you need history.)

Browser password managers are terrible as soon as you inch a tiny bit off of the "happy path" and need anything above "autofill the same password I used last time".