Why was the 13th amendment constructed with the exception clause which allows involuntary servitude as punishment for a crime? Also, why was the enforcement of this seemingly delegated to the states even though the amendment requires Congress to enforce it?

by 88_Vegan_Ninjas

I understand that the clause allowed for states to create hundreds of Petty crimes which resulted in Nearly 3500 people dying in Texas through its convict leasing program. As well as modern California saving upwards of $50million by leasing convicts as firefighters. It seems to me that without this clause states would not be so willing to arrest individuals as the cost would not be offset by various leasing programs.