Why is the delta wing naturally stable in pitch?
This is a very good question, as it shows some of the misunderstandings regarding "tailless" aircraft.  With deltas, one can consider them as blended wing/tails.

The function of a horizontal tail surface is pitch control.  The back of a delta is certainly large enough to do this. So much so, that now one can design
a forward canard to go with it.  This plane should pass the horizontal drop test (nose must go down).

Notice that birds, wanting more straight wing lift,
"unblend" a little and also have a fan tail.  Delta's do not generate as much lift as a comparable straight wing.

So designers can work with what they need, particularly with desired speed range.  Faster, the wings can pull in a little, as with the FB-111 swing wing.