It comes from a time when peasants couldn't afford to use certain letters due to excessive taxes on long names. The longer your name, the more prestige you had. A revolution was had and as a result, the two u's were agreed upon to be one letter as a compromise, saving everyone lots of money. This is also when the letter Thorn was dropped, as commoner and noble alike agreed that it was a thorn in their sides. Every time someone tried to open up a pub called 'Ye Olde Tavern' it would fail because snarky people would mob it crying out "Whateth beith thine 'Y', it shalth forever beith known 'Thorn'" and then they would promptly die because they had the plague.
There is no shame in not knowing; the shame lies in not finding out
