IME there usually isn't much contention looking at the same section of shelf. If I'm looking at the cured meats, I'm the only person looking at any shelves within 6ft either direction. Other nearby people are walking past, looking at shelves on the opposite side of the aisle, waiting for me to finish before checking the meats, etc. The algorithm doesn't have to optimize for literally every person/sale to still have a lot of impact.