Why can't conditional variables be "visual"? This is not clear to me - data flow and control flow are both visual (albeit their flavors of "parallel" composition and the like are incompatible, so they must never be conflated when shown diagrammatically) and conditional variables can be accounted for in control flow.
Say I have 100 rooms. Each room has 10 characteristics that might vary. Those 10 characteristics are going to be shown or referred to by about 10 different blocks... some are making decisions about the temperature, some are showing it on graphics, some are logging data.
That's 10,000 links. You can't actually draw lines for each of those links to the room information. It's literally impossible to put them on a screen, let alone process them visually. So you have to refer to the variables by name and you still end up with 100 links to draw between variable names and function blocks.
Once you refer to variables by name the relationship between the source and destination is no longer visual. The visual part is just inside any given encapsulated function. So now you're programming with parameter passing but instead of just typing text you're also pulling away to move the mouse and try to line blocks up on a grid all the time.
This should be pretty obvious while coding in text. Imagine every time a you call a function there has to be a line somewhere that represents that function call. It's too much visual information. You can abstract away some of it by saying "oh, we have a block here that goes out and grabs all the room numbers", but now a lot of the logic starts to depend on the contents of those blocks and it's no longer clearly visual.
Visual diagramming is great for roughing out an idea of how something works but enforcing a rigorous correspondence between the diagram and the function of the program turns out to be a lot of trouble for not very much gain.
