I fail to see it. Perhaps you can make the case for me.
*edit* also notice that there are several different questions here that are sometimes treated as one.
1) can one create a crypto where if the nsa spends 10 million dollars trying to figure out the transaction history of 1 single person they still will not be able to uncover that information.
2) can one create a crypto where it is prohibitively expensive for the nsa to uncover the transaction history of large groups of people.
3) every point on the sliding scale between these two extremes
When you send XMR from your wallet to someone, is that transaction sent in plain text?
When you connect to a mining pool, or even solo mining, is that communication ALL encrypted?
*sniff sniff*
Essentially the entire function of Monero is a cryptosystem that hides (i.e. encrypts) useful information about transactions such as who they are from, who they are to, their amounts, and their linkages with other tranactions.
You are looking at this at too low a level. There is no reason to encrypt node-to-node traffic because the assumption is that anyone can run a node (or see the same data on a block explorer, which is really a web view of a node).
The traffic is useless, however, in that it does not allow extracting useful financial information. It would be pretty dumb to create a privacy-enhanced coin where anyone can run a node and node traffic allows compromising your privacy.
i2p will be used to hide the fact that you are running a monero node at all, to provide a different sort of privacy. Really, though you could probably run in tails and hide that now (I haven't tried it).