They are transparent for more or less the same reason money bills have watermarks. Money has watermarks to make it harder for counterfeiters to produce counter

They are transparent for more or less the same reason money bills have watermarks. Money has watermarks to make it harder for counterfeiters to produce counterfeit money that looks like real money. Transparency makes it harder for counterfeiters to produce counterfeit dice that look like real dice, but aren’t fair.