They decided to switch to crypto because any payment system (like MIR or Golden Crown from Russia) is easily blocked by sanctions. BRICS members will not risk trading with Russia or Iran even if this payment system works better than SWIFT.
They've been at it for a decade or so now.
September 17, 2024 - BRICS is working towards the creation of a new payment system without the integration of the US dollar in its mechanism, confirmed Russian Foreign Minister Sergey Lavrov. The minister added that the new payment system will not only be used to settle cross-border transactions, it will act as a complete financial set-up.
BRICS Makes Major Announcement On New Payment System
https://watcher.guru/news/brics-makes-major-announcement-on-new-payment-system