Pondering the unanswerable

Why is it that my children dip their hands into every fountain they pass; jump into puddles large and small; squelch through dewy grass; will play with the hose for hours (if I allowed it); love the pool and the sea and the lake; in short, gleefully take every opportunity to make the biggest splash and get as wet as possible, but complain every time we tell them to take a shower and never, ever flush the toilet?