Simple. Christ fulfilled the passover which was initiated to point to His sacrificial atoning death for the forgiveness of sin. As He did so He initiated a new covenant for His people to be celebrated
Communion is not the passover celebration. That was done once a year on a specific date, communion is to be celebrated often. The physical elements are different as well. What one believes about the Lords Supper is not a salvation issue and there are wide variations even among Protestants. I love to discuss and support my position as it sharpens my study and belief. However I think this discussion among Christians should only take place after the basics of salvation are agreed upon something that is not true here
i think most of us can agree communion is for saved followers of Christ. Those on this forum cannot even agree what that is so we have bigger fish to fry. Salvation by grace through faith or salvation by works through Mary is an issue that determines where one spends eternity. What you believe about the Lords supper is not. I would love to debate my Christian brothers and sisters on this in a different forum where it is clear there is no daylight between us on the basics of salvation. it becomes a very different discussion with a very different tone at that point.
And yet NONE of these things are WRITTEN in the NT.
No WONDER there is such a 'difference of OPINION' about it all!