But with that said, one of those layers of defense is also using tools that are easy to keep secure so that the vulnerability doesn't appear in the first place. While Twilio isn't "a lone developer", I wouldn't be surprised if the person who did create that bucket on behalf of Twilio was just a lone developer fumbling around in the console. And again, that's no excuse, but it still is an area for improvement.
Now, as has been stated before, reading any cloud vendor documentation is like reading the Oracle manuals of years ago, not a happy experience.
Granted, these clouds now do things much more powerful and target more difficult enterprise scenarios. One can miss Heroku, and AWS has Elastic Beanstalk for that, but EB gets much more difficult fast.