TLS is computationally, temporally, environmentally, and financially expensive. Exhibit A. It’s also a bad solution: security is a transport problem, and should be solved at the the transport layer, not at the application layer.
Sven Slootweg has more on the subject of why ‘TLS everywhere’ policies — which are now, disastrously, to be enforced by browsers — are a bad idea.
A better solution is coming, in the form of MinimaLT. Until then, dpk.io is not available through any encrypted protocol.