I am going with your battery droping too much for the ignition to fire, but must ask how fast does it turn over ?
On a side line,
do hear the fuel pump tick a few times when you turn the ignition on ?
Just a silly one, you are holding the plug against the cylinder head, not the cam cover, it's rubber isolated.
Loose thoughts, if had been checking for sparks against the cover and this has been a red herring,
might be there is no fuel, as i say loose thoughts ....