Well, Shrove Tuesday immediately precedes Ash Wednesday, which in turn heralds the start of Lent, the Christian season supposed to replicate the Biblical story of Jesus Christ's withdrawal into the desert for 40 days and nights.
This is why Lent is traditionally a period of abstinence (which means a time when something is given up) and many people nowadays, including non-Christians, still get into the spirit of this season by giving up a particular treat.
In the olden days, with the awful prospect of 40 days of abstinence looming, it was perhaps a sensible approach to eat as much as possible just beforehand. Lent was much more strictly observed and was a time to eat much simpler food, and give up things like sweet, rich and dairy ingredients.