Many people don't survive, of course!
I think it must be something to do with the difference in size and the resistivity of the structures. Trees explode because the water inside them boils rapidly and produces steam. This is because the produce of Volts and Current (defined by the overall length and the resistance) - the Power Dissipated - is high enough to boil the relatively small amount of water in the tree. (Less water implies a higher resistivity)
For an animal body, the volts are lower (it's a shorter structure and the voltage relates to the Field times the length) and the resistance is much lower (mostly water with dissolved salts). This suggests to me that there will be less actual Power involved; not enough to actually boil your insides.
There is also the 'skin effect' which determines the depth at which a pulse of current or and AC signal passes through a conductor. It stays just on the surface of a very good conductor. I think, therefore, that there will be more current flowing through the inside of a tree than of a human.
Otoh, plants don't have a delicate nervous system and, if they don't actually explode, they tend to stay alive and produce green shoots from some of the shattered stump. Animal hearts can just stop from the electric shock.