Quite a few people involved in crypto send a bit of TOR noise across the wires using that client to do transactions
This is a good point, though. We need more and more things to use it (legitimately) so that the traffic alone isn't as suspect.
It'll always be a little suspect, I suppose, being only visible to exit nodes or whatever
(Still, it's great they have done that.)
Basically, using the TOR network as a VPN.
The TOR browser and Brave do the exact same thing, it's just that the TOR browser is configured to not store anything and to make sure it's fingerprint to other sites is as generic as possible (this is also why TOR warns you about changing window size, it un-generalizes that fingerprint). Both ultimately are conveniences because messing with SOCKS proxy settings is rather unfriendly for most users.
If you use a Linux distro, I'd recommend checking out torsocks[1], it's a shared library + a shell script that lets you "onion-ify" any application pretty easily.
[0]: This also means you can connect basically every mainstream browser to TOR if you know the port the SOCKS proxy is running on.
If it were directly using tor then I'd have to agree that most people wouldn't use it. Only those that are technical enough to understand what's going on and the security aspects. But they wouldn't be using Brave for the Tor functionality, they'd be using Tor Browser.