Question

why do veins have valves but arteries don 't have it?

Answer 1

In arteries blood flows under pressure due to being pumped by heart. But in veins the blood does not flow under pressure. Instead, there is risk of the blood flowing backwards. So, veins have valves to prevent the backward flow of blood while arteries don't

Answer 2

Because the function of valve is to prevent Blood From Back flowing This is because blood pressure in veins is very low (compared to arteries) as it is coming back from different organs.
There is no need of valves in the arteries because there is a maintained Blood Pressure.

I think So!!