[qb]

Why wasn't Circle using deposit networks? Did they take out private uninsured deposit insurance?

Circle's competitor Paxos is using IntraFi Network and Reich & Tang Deposit Solutions for BUSD according to their reports (https://paxos.com/wp-content/uploads/2023/03/BUSD-Monthly-St...) and has obtained insurance for most of their balances in excess of FDIC insurance limits.