I think it's less that "developers think this is okay", and more that this was an alpha stage project prior to the Reddit meltdown and influx a couple of months ago, and they've been working their asses off to keep the site up and stable, and are working to evolve the functionality to meet the need as soon as practical/possible.
mrbitterness
I would like to be able to turn off Random Magazines, Random Posts, and "turn on" Magazines I'm subscribed to on the sidebar. All of these as user options would be great.
I know there's a lot of work going on and I know all of these items come up fairly regularly, I'm relatively sure they'll be addressed in due course.
On Mastodon at least, neither authorized fetch, nor "disallow unauthenticated API requests" really stops the outflow. it does in an ActivityPub sense, however, I have both flags activated on my instance, but Mastodon has an RSS feed for every account, by just adding .rss to the profile URL, and anyone can pull that without authentication.
The option to turn off .rss feeds for accounts doesn't exist in a standard mastodon install. the Hometown fork of Mastodon has the option to disable it.
So while the flags above will help prevent random discovery/propagation by others on the Fediverse, there are still open doors for accessing the data, at least on Mastodon. I can't really speak for the other projects.
He's got 99 problems and well...