[kazinator]

Because the editing is at the character level.

If you look at the page source, this is what the grids look like for instance:

    +----+        +----+                                                                                                         
   /      \      /      \            .-----+-----+-----.                                                                         
  +        +----+        +----+      |     |     |     |          .-----+-----+-----+-----+                                      
   \      /      \      /      \     |     |     |     |         /     /     /     /     /                                       
    +----+        +----+        +    +-----+-----+-----+        +-----+-----+-----+-----+                                        
   /      \      /      \      /     |     |     |     |       /     /     /     /     /
  +        +----+        +----+      |     |     |     |      +-----+-----+-----+-----+
   \      /      \      /      \     +-----+-----+-----+     /     /     /     /     /
    +----+        +----+        +    |     |     |     |    +-----+-----+-----+-----+
          \      /      \      /     |     |     |     |   /     /     /     /     /
           +----+        +----+      '-----+-----+-----'  '-----+-----+-----+-----+

That's easy to change, but even for the top Vim slingers, it's not that ergonomic to produce by text editing.

You could benefit from tooling to produce the underlying ASCII diagrams; this tool is just a renderer to make them look nicer.

[sgoto]

Exactly.