Why is the ouput so low in this LC resonant circuit?
EDIT: I was hoping to see voltage amplification when the circuit was
  at resonance without using any active components, not even batteries,
  using only the input signal. Now I see that this is not possible in
  the shown circuit because of KVL and the diode drop.


Sure you can get voltage magnification with just a minor adjustment to your circuit. Consider this 2nd order low pass filter: -



It's frequency and step responses are: -



Pictures from This on-line calculator.

With the values shown (default ones that you can change - I changed the R value), I get a voltage magnification of 40 dB (100 times) at resonance. 

And, there are many variations on this theme including high pass and band pass but it comes with a price. That price is being able to drive a hard voltage signal at the input. 

Another version that provides high voltage multiplication is this: -