In general we do, because launching from west to east at the equator lets you use the Earth's rotation for a 465m/s speed boost. Launching the other direction m

In general we do, because launching from west to east at the equator lets you use the Earth's rotation for a 465m/s speed boost. Launching the other direction means you need an extra 465m/s just to counteract the rotation you started out with. Polar orbits don't gain or lose much from the rotation since they're aimed over the planet's poles.