I just don't understand that choice for either platform, is the intent not, biggest reach possible? locking potential viewers out is such a direct contradiction of that.
edit: seems its user choice to force login to view a post, which changes my mind significantly on if its a bad platform decision.
And yes, you can still inspect the post itself over the AT protocol: https://pdsls.dev/at://robpike.io/app.bsky.feed.post/3matwg6...
(You won't be able to read replies, or browse to the user's post feed, but you can at least see individual tweets. I still wrap links with s/x/fxtwitter/ though since it tends to be a better preview in e.g. discord.)
For bluesky, it seems to be a user choice thing, and a step between full-public and only-followers.
I'll (genuinely happily) change my opinion on this when it's possible to do twitter-like microblogging via ATproto without needing any infra from bluesky tye company. I hear there are independent implementations being built, so hopefully that will be soon.