Here's a few things that I've seen:
1. At the youngest age (u8-u10) the best keeper is also the best field player. They are the aggressive kid that has no fear. They are good at any sport they play. The coach likes them in goal because it gives them a good chance to win, but also plays them on the field because they dominate on the field too. The parents don't want this kid being a full time goalie.
2. Or at these ages, a coach will rotate several players in goal. The lose some games because of it. Parents get upset and say "if we just had a full time keeper, we'd never lose."
3. Or during the first few weeks of a new season, the coach says "who wants to play in goal?" And 3 kids raise their hand. Not really knowing what it means to play in goal. They either really like the position or they don't really care for running or they are trying to be a team player. One of these kids winds up being a full time goalie halfway through the season but she doesn't really like it. The coach either doesn't know or doesn't care and keeps her in goal. The parents get mad because they spent $2,500 for their kid to move 14 yards every weekend, while they drive 30-60 minutes to watch her stand around in a long sleeved shirt for 85% of the game.