There is no signature, there is no proof of identity of the signing party (copy of personal ID, witness, ...). Usually no confirmation that other side also accepted it. No copy of ToS received after "accepting". We all know that it could be that, for example, my 4yo child clicked on it when I went to the toilet after reading first few paragraphs of ToS, and now I'm somehow bound to it? Also, it happens very frequently that you "accept" some ToS, and after two years you find on some forum that Google, or PayPal just changed their ToS without sending you the updated copy for acceptance.
Sorry, but too many things that are really different between ToS and a real acceptance of a Contract.