I'll agree that graphical languages don't seem to have caught on for general purpose programming, but some reasonably powerful ones certainly exist at this point.
Speculating as to why, I admit I have no intention of picking up a graphical language for my next project. Partly it's familiarity (I don't know what I'm missing), partly it's learning curve (expending effort when my current tools already work), and there's definitely concern about the ecosystem (manually writing bindings is never fun). There are also existing tools whose functionality overlaps to some extent - I've seen (and briefly played with) tools for some languages that will create flow diagrams from your source code. It seems like graphic-centric languages exist, but only gain widespread adoption for specific tasks that are frustrating or tedious to address without them.
When I had to suffer through LabVIEW (2009ish) my notion was that it LabVIEW-the-language might have potential to be a decent language, and that it was a shame that the only possible IDE for it (LabVIEW-the-program) was so horrible. The expensive license can't be helping mindshare, either.
(Now, that was long enough ago that I forget most of my specific opinions, and many of them are probably now outdated.)
I believe I was primarily using Architexa (https://github.com/i3labs/architexa), but it was a number of years ago when I was working exclusively in Java.
JetBrains also provides a few diagramming plugins, but I've never used them.
I haven't yet come across tooling that does the same for C, C++, or D. This response inspired me to take a look though, and I did find something for Python (https://stackoverflow.com/questions/45238329). Thinking about it, the instrumentation approach taken there might actually work fairly well for most systems languages assuming you don't have any dead (or rarely called) code. Graphviz could be combined with the "-finstrument-functions" GCC flag and a few supporting data structures. Templated code would be tricky to deal with though.
