But why?

www.liverpoolmuseums.org.uk/picture-of-month/displaypicture.aspx?id=108

So, there is a great story behind this painting: "The painting is believed to be the result of a challenge between father, William Nicholson, and son. Nicholson senior, whilst looking at one of his son's works showing a single jug, commented, 'but why one jug?' to which his son, Ben, replied 'well, why don't you paint a hundred?' Here we see the result - Nicholson's still-life 'tour de force'."

Why did he have this many jugs? In part, because of his still life paintings.

"The jugs, mainly English pottery and some china ones, were an important part of Nicholson's life. They adorned the surroundings in which he lived. His son, Ben, later admitted, 'But of course I owe a lot to my father - especially his poetic ideal and his still-life theme. That didn't come from Cubism as some people think, but from my father - not only from what he did as a painter, but from the beautiful striped and spotted jugs and mugs and goblets…. which he collected. Having those things throughout the house was an unforgettable early experience for me'. (Sunday Times, 26th April 1963)."