Nostr isn't a guaranteed success and is already showing signs of stress. I''m bullish on its potential, but it's understandable for them to explore other solutions. More options for users, is a win for everyone.
Rumble have confirmed that their wallet is on the way, could have just added nostr:npub19hg5pj5qmd3teumh6ld7drfz49d65sw3n3d5jud8sgz27avkq5dqm7yv9p and open it up to a host of wallets, but I doubt they're going to be that bold
https://cryptoslate.com/rumble-bets-on-bitcoin-with-new-creator-payment-wallet/
Discussion
I agree theres work to be done but how do you test its limits without putting it under strain? Since its an open protocol it can be part of your various payment options not the only one
I've only read that they announced support for Bitcoin, but not Lightning. I'm guessing most Rumble users who have Bitcoin or use Lightning aren't on Nostr. Meanwhile, users on Nostr are struggling with NWC connections.
Tether's subsidiary Synonym is developing Bitkit and Pubkey Core. They will probably have deep integrations in the near future.