The Shulchan Aruch in siman 469 and 476 lays out the concerns we have that someone might mistake you main course for a real Korban Pesach. This includes not saying 'this meat is for Peasach' and not eating certain foods roasted. Some Achronim there extend these enactments even further, the details of which are not my concern here.
My question is why are we so concerned about mixing up the meat with a real Korban? To put it in perspective, we don't find an concern on Succos or Shvuos that one might think you are eating a Shlamim. So why here?