I think your question is perfectly valid and not offensive at all.
In many cases, the "look" outweighs some other things, so a child who is a better singer with a completely wrong "look" will not get cast, and a weaker singer will be. Also, for tours, they not only have to find 7 girls who can sing their roles, but they have to find 7 girls with parents who are willing to commit to the grueling schedule of a tour! I think this probably limits their options severely, whereas in a Broadway show, more families would be willing to uproot themselves and move to NYC, knowing that they will be staying in one place. Does that make sense?
I know that when I auditioned for the Sound of Music Asia tour (and keep in mind, Annie is probably going to China in the summer, so it's a similar situation), the turnout of kids auditioning was not as large as one might have expected, because there are many families that support their children in theatre, but cannot go on tour -- families with two working parents who can't leave their jobs or telecommute, for example.
Also, in the case of non-Equity tours, the child is getting paid plus per diem, but the parent is only getting per diem. The child's salary is very low for theatre, while the family might also be losing money from the parent chaperone who is no longer making a salary (quitting job, taking an unpaid leave, etc). So ... many families with potentially great Annies would not be able to accept the role just due to their situation, which would make the casting directors ask the second choice Annie, then the third, and so on.
I also think that the popular music of today has a (negative) affect on kids who grow up wanting to sing. Back when Annie first opened on Broadway, we didn't have the music of today, with so many electronic effects that practically anyone who wants to can "be" a singer and sound decent. I think because voices were less manipulated back then, kids listened to singers and aspired to sing like their favorite singers, who were better "vocal role models," if that makes sense. We don't have that anymore -- the good vocal role models in music that is new/popular are pretty much of the past.