So we cant set our own password? I just created an account, your site generates a password for me and I thought I can change it as what I wish when I'm logging in but I don't find any ways to set new password as I wish. Indeed there is a way to change password but it is still generated automatically by your system. I think there should be a way to change the password as we wish because it will be easier for user to remember the password.
The most likely reasoning for this is that it would be harder for possible hackers to get into your account, it's better to have a stronger password and knowing some people will put like password123, so in conclusion its for security reasons in my opinion.