Question

why cant matter can be created and destroyed?

Answer 1

that's just how it is
can u think of any example in which u could destroy matter or create matter?

Answer 2

According to the Energy-mass equivalent relation of Einstein, E=mc^2, matter can be changed into energy and vice versa. This shows that once you got a mass, you no longer would be able to destroy it. Because it always exists and it is either in the matter form or in energy state and there is nothing to talk about different forms.
I hope it does make sense.