With his apes dying from the hands of his younger brother, he learned that he could summon them again at will for as long as he had a World Energy to waste.
Not only that, he learned as well that he could let all his tamed beast stay inside his body just like how his Blood Minions could stay inside of him. Just thinking about it could make Jim realize how useful it was particularly in a real battle.
Most of the Beast Tamers didn't have such ability just like Jim. Their tamed beasts were always with them all the time, not inside their body. So Beast Tamers didn't really have so many tamed beasts with them for they couldn't always bring all those beasts all the time.
Some of the Beast Tamers had a useful artifact that could contain many beasts inside just like Jim's mother, Charley, who had a strange book of where her tamed beasts were resting inside.
