Now back to the questions of "Why do this if Tor already exists?" and "What inherit benefit would this have for bitcoin, why does bitcoin need this ability?"
I don't have an answer other than it sounds fun, and I suppose it doesn't need this but I don't think it would be detrimental to bitcoin if it had this ability either, if anything it just adds additional functionality and creates an alternative to Tor hidden services. Mostly I just think it would be really cool to host a blog or something on the bitcoin network.
At very least, it'd increase burden of running full node and development of full node software (Bitcoin Core, btcd, gocoin, etc.).
It can't be currently implemented on every node, because Bitcoin nodes don't talk end-to-end encrypted, and end-to-end encryption is necessary to insure anonymity. Such feature would require change in the way they communicate. It'd be better if, instead of changing Bitcoin Core, you just installed an addon.
FYI, it was proposed under BIP 151. Although it was withdrawn on 2019.