Why positive is greater than negative?

Answer 1

A number A is said to be greater than another number B is A - B is more than 0.

If A is positive and B is negative, then A - B is always positive and so each positive number is greater than each negative number.

Answer 2

Think of the temperature scale.

Comfortable air temperature may be say (+)16 oC , but a very cold air temperature may be say -20 oC

The figure is greater but the temperature is much less.

So think of numbers in the same way.