My understanding is that the hinges are sealed but the rollers are not. The rollers are on the outside of the hinges. Sorry for the non-technical description. As I have been learning more about chains recently it has changed my thoughts on lubes. We need something thin enough at first to penetrate under the rollers and then stay there to lubricate.With an o-ring, x-ring chain you do not get any lube under the rollers. ie sealed chain. They are pre greased and sealed with the rings.
Fortnine did a quasi-scientific comparison of lubes including a friction test. Plain oil did extremely well, probably because it seeps into those tight rollers. There is a good description in the first 3 minutes of the video, but here he shows exactly where our manual lube needs to get into.
In this diagram, part 5 is the roller and it rolls around part 4 (and the barrel on part 2). The lube needs to be in that tiny space, and it gets there when we apply lube manually. The sealed lube is between part 3 and the inside of part 4. From https://en.wikipedia.org/wiki/Roller_chain
The cross section in this article shows another view. 1.3.2 Sealed Roller Chain
And in this drawing the green and blue barrels are rollers. You can see the x and o rings don't trap lube for the rollers, just in the hinge. https://en.wikipedia.org/wiki/O-ring_chain