Getting kids to wear a cup

Our Little League requires all 8u players to wear a protective cup. I have sent this message to the parents multiple times and even sent a link to a specific product on Amazon. However, after repeat attempts, only three kids are wearing a cup to practice. This league does not have any stealing, so the catcher is not as important, so I'd rather use a strong defensive player in the field.

Has anyone else had this issue? Any tips to convince parents?

My daughter is playing softball in the same league and their rules for protective face guards are optional. Yet, her entire team is wearing one which I find very interesting as a comparison.

I want the players to be safe, and also want the flexibility of putting together the most competitive lineup as possible, so this is a very frustrating issue. I'm starting to feel a bit weird continuing to ask them to buy one to no avail.