Don't kid yourself, it wasn't due to size, it was due to skill. better kids come to tryouts every year and take spots from other kids.

I believe that is what travel lacrosse is all about, picking the most talented players. plenty of smaller kids playing on top teams. just admit it that you are not happy that your son didn't make a team and you are blaming it on size.
have realistic expectations for your son and you will not have to bad mouth several programs that passed on your kid