I see there are already a ton of replies about push vs pull but the other (non-technical) aspect of a newsletter is the expected cadence of publishing. Some blogs have long gaps between posts and others have multiple posts per day. Newsletters typically define a daily or weekly schedule and stick to it. Sure, a blog could do the same thing, but they generally don’t. It sometimes feels like the difference between Last Week Tonight and a constant feed of breaking news clips.
Yes, looking at the technical differences is missing the point.
Newsletters tend to have a regular schedule, are easier for consumers to get started with (everyone uses email already), and have revenue models that can make it sustainable for the creator.