I'm not certain I agree, John. On the most basic level, the pivots must contain parts that make contact with one another, or else they would be suspended in midair, which we both know they're not. And if they contain parts that make contact with one another, then those parts create friction when they move, which slows the action of the derailleur. A lubricant reduces this friction, particularly one containing a penetrant that allows the lubricant to work its way through what you're describing as the cracks of the pivots, and into the pivots themselves. As to whether or not a lube will attract dirt, the lube I used contains particles that are much finer than particles of dirt, and as I already described, is conveyed into the pivots by a penetrant carrier fluid, allowing it to reach places that dirt can't. It then lubes the pivots, but also acts as a seal that keeps dirt on the outside of the pivot, As a result, the derailleur may appear dirtier on the outside, but is actually cleaner and more protected on the inside. The dirt can be easily wiped off. Last but not least, keep in mind that we began with a very dirty derailleur that we stripped clean using a powerful degreaser. It stands to reason that it would need to be lubed after that kind of treatment. If you look around online, I think you'll find a lot of authoritative supporting evidence for what I'm describing here....
How To Clean and Lubricate a Rear Derailleur