These protocols exist, e.g. on top of I2P network.

Thing is, nobody has any incentive to back them.

IMO, I2P and Tor were never a solution to this, they are anonymization networks, which adds their own requirement on how to use it, and most people don't need anonymization. These protocols are slow and complex, thus not user friendly.

Maybe aiming a lower tier of security (like what TLS offers) is good enough for regular user. For example, Matrix or Jami.

But the problem with Matrix and Jami is that these are still too complex for regular user. No user, no motivation for the developer and it's a downward spiral from there.

And worse, given how they work, there is a disincentive to use them ( especially so in US jurisdiction ).