The browser profile is harder to exfiltrate, in part because modern OSes have ways to restrict access to particular processes, but that was also only part of the benefit: the main thing is the duration of the session. Tons of people leave AWS keys sitting around in ~/.aws for ages.
You can setup schemes with STS but not everyone remembers that and with this approach you have a very simple answer: it always uses STS, there's never a file sitting around for someone to accidentally save somewhere they shouldn't, etc.
Nothing here is something you couldn't do on your own — it's just a very easy option with safe defaults.
Or perhaps even entirely useless if you'd normally use it as part of a local build and test process.