duz anyone know why the microwave spins
Well I hope that your MICROWAVE doesn't spin when running!?!!
The little table inside might spin though, and that's to distribute the beam more evenly onto whatever's sitting on the turntable.
Otherwise you can get uneven cooking of items, which is, of course, undesirable.
(FYI: Back in the early days of microwave cooking you had to cook for shorter periods and rotate the plate of food every so often
by hand to circumvent this problem....)