First of all, the ships in star wars have shields meant to stop energy lasers, not kinetic forces (a La asteroids, mass drivers, other ships)
And seeing as pretty much every UNSC ship has a MAC cannon, shields are useless. And if that fails, the ships can always detonate their reactors and take them down with them. HALO FTW
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Actually, even in the movies where everything is relatively weak, you see huge asteroids bouncing off of the star destroyer shields.