Because I was thinking (or, more probably, not thinking at all) like a nice Catholic girl instead of paying attention. "Eucharist", in this context, is just plain wrong.
The original Last Supper was a Passover meal. Jesus and all of his disciples were Jewish. They wouldn't have had a single clue about naming a Blessed Sacrament that was being invented as they supped. Some of us refer to the Last Supper as the first celebration of the Eucharist (now), but those participating in the actual event certainly did not.
In fact, Jesus himself is quoted referring to the Last Supper as Passover, not once, not twice, but three times in the Gospel of St. Luke, alone. (Luke 22:11; 22:13; 22:15).
Additionally, the synoptic Gospels all refer to unleavened bread and sacrificial lamb, as well as outlining the structure of the Passover meal. In New Testament accounts, the Last Supper clearly follows prescribed seder guidelines for eating, drinking, singing and praying.
To be completely fair, a few historical discrepancies exist in dating the eve of the Last Supper. Whether or not it actually took place on Passover or a day or two beforehand, and whether or not the actual date was "tinkered" with, are both matters of some debate. None of this, however, excuses my words that Jesus and his disciples celebrated the Eucharist during their final meal together.
Any idiot could have cracked open a Bible and seen all of this but, apparently, I was an exceptional idiot on the day I used the word "Eucharist".