I am a platinum premier elite member and I never got offered the spring 2013 mega bonus offer. I only found out there was an offer as a coworker of mine (also platinum premier elite) told me he received a bonus. Do they offer different promotions to different members? We are both platinum premier elite. Why would hey send one member a promotion and not the other member?
I did receive the fall mega bonus within my Marriott rewards account and I registered. I remember a time when Marriott used to automatically register me...I guess that's not the case anymore.
I can't speak for you directly, but I am informed of these promotions via email. I get the emails from Marriott because I check the box to receive them. So perhaps you've opted out of email notification, or perhaps your Marriott emails are getting routed into your Spam folder. But everyone gets these emails just the same.
Via the email, there is a link that registers you; you do not get automatically registered.