NSmith...

Probably because Maltitol is used for two purposes. The primary one is to sweeten and it would take more Maltitol to sweeten unsweetened chocolate than it would a protein bar which also often has glycerin in it as well. I'm sure you've noticed that the protein bars are not as sweet generally as a low carb chocolate bar. The other purpose for Maltitol is to give the product that creamy "mouth feel" that everyone associates with chocolate.