Because most coaches know that they cannot teach or develop anyone in such a short time, and all they want is to build some chemistry for the teams. Many have HS tournament games the very next week. These HS training sessions are light duty, low quality training anyway so all the players know going in.
As for training in club, don't you mean for the past 10 months? You guys actually take 2 months off???
Last, many schools have been training since Sept as soccer is a PE class. It would simply be a continuation of that. My kids HS just finished tryouts last Thurs and practice starts today. Unfortunately, between the league playoffs, TG tournament and CRL games, they will do both club and HS training for the next couple of weeks still... Oh yeah, school work is in there somewhere too!