One of the reasons they are hard to get in is you can not get as much leverage on the short side as you can on the long side. Another reason is most of us remove the oil baffle that is stuck in the axle housing on both sides. It is a round, stamped steel disc with a hole in the middle that is a bit bigger then the axle. It was put in at the factory for two reasons, 1. To keep the gear oil from sloshing as fast all the way to the axle seal 2. To help align the axle with the third member.

One of the reasons it is so easy to get the axles into a Diamond housing is it has two seals, the stock one in the ball and one by the diff.