Reporting for RSVP only works from email sendouts. The webpage version of emails isn't able to capture reporting info. The RSVP block is specifically built with the functionality of email click reporting in mind, and thus is only feasible to send to contacts. RSVP reporting for emails is kept as a distinct section in the email report. 

If you need the ability to RSVP for non-contacts, then I'd advise using a survey page, lead generation landing page, or event registration.