...only a few boys volunteered....
&&&
I am willing to bet that there would have been more boys interested if it was open to boys only.
I agree with that but I think it is also just part of the equation. When I was young it was a PRIVILEGE to be an altar boy.
I had a trial period and I was only accepted after I showed that I could do all of the prayers & responses and learn all of the tasks in serving the priests. I think when something is a challenge boys are more eager to be a part of it. If it is something anyone can do, why bother?