2 - Even in still conditions, I prefer the heft of a solid object to a flimsy sheet of paper.
3 - Tablets are much more readable in low light, as you can bring your torch or candle close to the surface to better illuminate it. Try doing that with a sheet of paper - you won't try it a second time!
4 - Tablets are much more secure. You can just scrape the ink off of a piece of paper and write anything in its place - a securely baked tablet can be destroyed, but it can't be rewritten.
5 - As a corollary, writing on tablets concentrates the mind. Once you've put your tablet in the oven, it's done; no regrets, no scraping off the ink.
6 - Tablets are much more durable. In proper storage conditions, they could last thousands of years.
7 - I already have the materials I need to make as many tablets as I want - whittled sticks, a good oven, and honest Euphrates mud. Why should I invest in a new set of tools, spend hours in the messy and unreliable business of making ink, and make myself dependent on Egyptian imports for my writing surface?
People are talking up the new medium's portability and flexibility, but I think it's doomed to failure unless it can address these shortcomings.