What you're forgetting is that SU one is dropped in base and thus cannot be stolen and works even without a fuel point, whereas the Axis supply drop will always be near the frontline and needs a point.
Do you drop ammo/fuel when you know you might lose a point? I don't think so.
Dropping is base isnt advantage at all. You need to retreat 1 squad from battlefield to pick it.
What's more, you sacrafice ammo - no demos, no mines, etc etc
Sacraficing MP is more fexible cause you still have ammo for upgrades and other stuff. You just need to play carefuly so protect from MP bleed so you can float XXX useless MP.