Yes, you do have to create an account – there are many reasons for this, one of them being reduced risk of data loss due to forgotten initial password. Yes, it does happen. With the account setup procedure we get a better chance of informing users of the importance of the password, and it has to be typed 3 times before actually encrypting anything.
It also enables us to do some other cool things. Part of the technical background can be read here: https://www.axcrypt.net/blog/what-is-an-axcrypt-id/ .
When you are “signed in” to AxCrypt, the most important aspect is that you’ve established a verified (checked against the one you initially set) default password to use. This also reduces data loss due to typos when encrypting. Yes, it does happen. The password you signed in with is then used to decrypt and encrypt all files (until changed).