Question

if gravitation force acts between all objects why don't they move towards each other?

Answer 1

Since their masses are very low, the overall gravitational force exerted by then on each other is very negligible. Hence they don't attract each other even though they're actually exerting a force.
hope it helps

Answer 2

The gravitational force is very weak, hence objects kept on a surface don't move torwards each others.
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