It is incredibly dangerous to the integrity of your block to try heating it with a torch.
If you really must heat anything just heat the actual plug... this usually squeezes the rust and corrosion ( let cool before trying to take it out ) and makes it possible to get it out....
The block is cast iron... known for needing even heating and cooling in order to avoid cracking....
Many may have thought they actually got the block area hot enough to help them remove it... and may not have been computing the convectional heat loss.... ( ie, they really did not heat it enough to make any difference to the plug ) but thought they did... where actually heating only the small plug has a shot at heat expansion worth trying... and if it happens to be cast iron itself you can easily replace it if it cracks.... unlike the engine block..

Do I need to mention that antiseize should be placed on the threads of whatever goes back into this hole ?