Why would a judge order $ 20,000 bail for 5 Islamic radicals that were arrested at the New Mexico compound starving and training children to preform

Bail is a guarantee of appearance at future proceedings. Several factors are taken into account. Level of violence (the 'school shooting" thing is the account of one foster parent who 'heard' her charge mention it), financial means, likelihood of fleeing and possible accomplices.

20K seems low, but it must have been set in agreement with the state as well as the defense.