It's a token on the Ethereum network, currently going for $0.16. The Brave browser has a native BAT wallet, that allows you to pay sites directly or in this case, the video creators. It's a way to do seamless micropayments via your browser without payment providers.
If even 1% of viewers on YouTube awarded BATs to their preferred YouTubers, the content creators would have no problem operating within the infrastructure. Suppose the person you're donating to does not own such a wallet. How is the payment processed then?
So, BAT is currently useless for the majority of active YouTube content creators. It's one thing if you can't donate it because you don't own the wallet. It's another to not be able to receive it.
Sure, that makes sense. I wonder how many YouTubers of any merit would care (due to Patreon), aren't aware of BAT or simply don't realize how cryptocurrency works and become confused by the whole ordeal. Patreon pays actual USD that you don't have to exchange at a fluctuating rate.