Thank you for asking!
Actually, AxCrypt 1.x also worked like this, but it was optional. There are two checkboxes “Remember this passphrase for decryption” and “Remember this passphrase for encryption” in AxCrypt 1.x that corresponds more or less to the way AxCrypt 2 works.
We’re trying to make it even easier to use, and with less risk of mistyping and thus perhaps not being able to open files. That’s why we’ve developed the “sign in” model, which is also a commonly used metaphor for many softwares and services, and thus easy to understand for most users.
The “sign in” model to AxCrypt also makes it possible for us to really verify that you have typed the correct password, and when you encrypt files, there is thus no risk that you happened to make a mistake this time.