I like how they phrase this like it's a considerate product decision, while it's essentially them not wanting to shoulder the expense of storage. Without knowing more about their product internals an immediately obvious and important feature getting the axe from this is highlights. Example: I will stream and then go back the next day and cut the video down and take the snippets and post them to youtube. These highlights then lead to interest in the channel which leads to more viewers. Now I need to archive all my stuff locally, and upload it over my mediocre connection. If they limited the archival time window to 4 hours after the end of the broadcast they would have their drastic reduction in infrastructure cost while not totally removing a valid and arguably important feature.
I think that's how Twitch works by default now. They archive the whole stream for like a week so you can Highlight it, and then it's auto-deleted (unless you've configured it to keep everything).
I believe the default now is that nothing is saved, not even for a week. However, each user can configure a setting that does cause Twitch to save the stream for about a week, before it's deleted.
In order to fully archive a stream "permanently", a user needs to view each archived recording individually and select an option from that page to save it forever.
