the email generated by the registration is a plain text email, this is why the link is not clickable, it uses a plain text email format to prevent the email message from being ttreated as spam.
you can edit the email template:
WA_UniversalEmail/Email_Templates/registration.php
change:
<?php echo($WAGLOBAL_Root_URL); ?>users_profile.php
to:
<a href="<?php echo($WAGLOBAL_Root_URL); ?>users_profile.php"><?php echo($WAGLOBAL_Root_URL); ?>users_profile.php</a>
to convert it to a clickable link.