Probably because the Rebels had just startted supplying the base (it WAS a relatively new base, and it takes time to move in all the neccessary supplies and shit without remaining detected.) and at least one of the more recent shipments (the attack on Derra IV from the TESB Radio drama) got wiped out by the Empire prior to the battle of Hoth. That took out a healthy chunk of their supplies, as well as at least another starfighter squadron that was to be assigned there.Batman wrote: I don't see why. Yes, so the Rebel Snowspeeders did mostly dick against the AT-ATs. That's most likely because they weren't designed to. Given the minuscule size of protorps and the accompanying launchers I fail to see why they can't be mounted on purely atmospheric vehicles (as evidenced by the fact that real-life combat aircraft regularly carry weapons significantly larger than that). Assuming no starfighters=no aerial threat worth mentioning is IMHO foolish.
In any case, they evidently had some explosives, but either the delivery mechanism wasn't workable or they lacked the power to penetrate the armor.
And while we know (Isard's Revenge) that large torpedoes could fuck over an At-AT (and something of the yield of a proton grenade could probably do so too, since they can supposedly damage starfighters), that doesnt tell us how many would be required- smaller torps (like the micro-torpedoes the spacetroopers use) are of course correspondingly less powerful.