This number is considerably high considering that the national average for number of inmates, parolees, and individuals on community supervision are around 4.5 Million people. So from 50 states, Texas held around 9-10% of the offenders.
The numbers above represents not only the convicts who are thrown in jail. Those who are under house arrest (with ankle monitor) and those who are forced to do community service as a form of punishment are also included.
I think because no other country in the world has created something interesting or it was just a pass down by their ancestors and they wanted it to be a thing