I would presume zone blocking. Zone blocking requires artificial intelligence to be programmed to determine who to block on a given play. Of course, we see the results of that this year with the blocking AI (which is particularly interesting to watch on Zone blocking plays). Manual L/R slide requires no intelligence, just a direction to go/follow.
Again, I think this goes back to fundamental design. I don't believe they intend for slide protection to do anything on running plays. So it's not "broken", and I don't really think it's something they play to do either. You never know, but I wouldn't think so.
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