The "Limit number of images in a page" section says "Ideally, a page should have no more than 100 images (regardless of how small)." What is the logic behind this recommendation?
Topic on Talk:Recommendations for mobile friendly articles on Wikimedia wikis
This relates to the prior statement Because the mobile site lazy loads images, articles with large numbers of images will timeout on mobile. The number of round trip requests between the browser and the servers to fetch the images becomes a performance issue.
But why 100, and not 75 or 500? Is it just an arbitrary selection?
I would guess it was a relatively arbitrarily chosen number, but was probably at least informed by some experimental testing. The mention of 10,000 images in the same area makes me think the author was thinking about orders of magnitude when giving the advice. This is all speculation of course by me.