If you click on this link at the top of the page you can enter a new email address other than the one that you registered with.
I would suggest setting up an email address specifically for PC Advisor replies, then don't check that account for mail unless you wish to, just clear out the mail box once in a while.
You could, I suppose, set up a spurious email address, but that might cause problems for PC Advisor as the automatic responses would keep getting bounced back. You would have to wait for the Forum Editor's response on that.
Why is there no way to change the option at the moment? Because that is the way it is. Too many people forget that this site is provided free of charge as a service for PCA readers, and make demands on the FE. There is nothing wrong with making polite request, but it costs time and money to make changes.
Others have probably made the same request as you before, so the FE will be aware of the issue.