Well, 48 photograph thumbnails, frame images, and complex tabling, not to mention other images, can certainly lead to a slow experience while browsing, especially
while using a Mac browser. Since that situation is already bad enough, I can only imagine Apple's reasoning in this is that they don't want it to seem any worse.
Of course, it still kinda sucks that they made that decision for you, but if you can't make your own photo galleries, you'll just have to live with this limitation until Apple changes it. I point you to the iPhoto feedback page.