It’s a little odd as as well. If your pet dies and the body despawns, the macro system cannot tell it’s dead anymore and thinks you just have no pet out. Resurrecting at a graveyard or dungeon start after a wipe for example.
Pretty sure this is how I used to have it when I played hunter a lot. If the default logic fails because the pet’s body is gone, you can just right click it to revive your pet. 
#showtooltip [@pet, dead] Revive Pet; [nopet] Call Pet 1; Dismiss Pet
/cast [button:2] Revive Pet
/stopmacro [button:2]
/cast [@pet, dead] Revive Pet; [nopet] Call Pet 1; Dismiss Pet