What could be the reason that jack and Jill fell down?

It has also been suggested that the rhyme records the attempt by King Charles I to reform the taxes on liquid measures. He was blocked by Parliament, so subsequently ordered that the volume of a Jack (1/2 pint) be reduced, but the tax remained the same. This meant that he still received more tax, despite Parliament's veto. Hence "Jack fell down and broke his crown" (many pint glasses in the UK still have a line marking the 1/2 pint level with a crown above it) "and Jill came tumbling after". The reference to "Jill", (actually a "gill", or 1/4 pint) is said to reflect that the gill dropped in volume as a consequence