Unable to login with password saved in 1Password after changing to generated password

Actually I just read "Use the password generator to change and strengthen your passwords." I'm having trouble understanding why changing a password in the browser has two steps, and in the app it has 4. Why in the app do you have a whole step involving copying and pasting the old password (and this doesn't need to happen in the browser?)? And the instructions to "adjust the settings to the website requirement" need to happen in the app but not the browser? Why would this be?