It’s pretty simple, really — you use up all of the butter and sugar, luxuries you’re supposed to forsake during Lent.
It’s kind of amusing to me that Catholics throw the biggest party on the planet, and Anglicans make pancakes.
Well.. maybe in part that’s due to the difference between being Anglican and Roman Catholic. We Anglicans are not entirely unhappy with this, mind you — though I’d love to be rid of the Shrove Tuesday post-dinner stomach-ache: my first penance of Lent?