Because "that" is only a four letter word you learn when you're little so you don't have to continue pointing at things you want. You can say "that" and not "das".

Why do trees have bark?

Dave

because they evolved from dogs

Is there a Chrysanthedad, as well as a Chrysanthemum?

Yes in fairy land

Why is milk white ?

it's a marketing ploy, if was it's natural colour of black, it wouldn't sell very well

why is coffee black?

Because you forgot the milk

Why is the road dark grey ?

it's not - that's the tarmac

who invented the roundabout?

zebedee

what are those white lines in the middle of the road for?

drunk people to walk along

why does the traffic cone look like it does?

Because they don't look like anything else

Why does the Sun burn if you stay out in it in the Summer ?

because it's beyond boiling point hot

why do people like to sit out in the sun to burn?