The .357 Sig round was developed by Sig to be the next, latest and greatest round for law enforcement. Like the .40 S&W did a few years ago.
Great round, but since it never caught on with the majority of LE agencies, it is very very expensive.
Its the issued round for the Secret Service and Air Marshals.
But, since its the Feds buying and they could care less about how they spend our money, that’s what we get.
Per a thread on a LE forum from 2007, most SSA agents are former Secret Service, which explains the choice of round.