Stuff Expands to Fill Available Space

My darling son delivered a glass door Ikea cabinet. I put it together and somehow it was immediately full. How does this happen?

My Silkstones, once all on one shelf, can now be enjoyed without climbing on a ladder. The Tiny Kitty dolls, the oldest of my fashion doll collections, are now visible to the naked eye. They're in holiday red from last December. I couldn't see them anyway so what difference did it make? Poor neglected Cissette still stands on a bottom shelf. To see their faces you must get on your knees. It's a spiritual experience.
Monster sized Cissy dolls had their own shelf until some of the Silkies moved in. It was actually the Cissy's fault that I had to get this cabinet in the first place. Too big to fit anywhere else, they kept whispering, "If not now, when?" Hopeless.
Of course now that there are a few inches of space here and there, I'm making lists of what dolls to add. It never ends.