Why do top companies hire on the basis of experience in terms of years? Why not on the basis of knowledge and skill?

Not only years, we hier based on actual experience , knowledge , salary range , personal qualities.All this gives good idea about the employee and his capabilites.

thanks

Because knowledge of difficulties and ambiguities encountered in practical life/work can come only with experience and cannot be taught in school. That is why experienced one can tackle with all those problems rather easily.

SIMPLY BECAUSE BY  EXPERIENCE WE CAN LEARN MORE THAT CAN AMELIORATE OUR KNOWLEDGE AND SKILLS 

 as experince comes from knowledge and more work