The registered email address creates a second point of security. Let's say someone finds out your username and password - they can then block you from using your account by changing the password. But then you can get the account back by requesting a password reset to your email. In order for a person to gain full control, they need access to your email address and not just your TLOPO account. So, allowing a person to change the email within the TLOPO account itself makes your account very vulnerable.
If you happen to need an email change, feel free to send an email to support@tlopo.com.
