When the King beyond the wall attacked the wall why did he only send around a 1000 men if he had a 100,000?
The King beyond the wall had a large number of followers, but they were wildlings, not soldiers. Sending a horde of badly armed unarmoured "civilian" wildlings at a well defended gate would have blocked it with dead in no time.
A much better strategy is to pick your best fighters (and giants) and let them open the gate and clear the defenders. Then bring through the masses.