I don't use it because at this point it's alien in the world of modern computers. Back when Smalltalk was in its prime it wasn't just a programming language, it was essentially your operating system, complete with its own graphics system, window manager, etc. This hasn't changed, but instead of being the basis of your system it's essentially another OS running on top of whatever your poison of choice is.
I think today the concept of the Smalltalk image and workspace has pretty much killed it, not the language itself. I use git for version control, I use GNOME as my desktop environment and IntelliJ as my IDE of choice, trying to do anything in smalltalk requires I transport myself back to the 90's.
GNU smalltalk is the closest we have to a smalltalk implementation that works well in modern computing environments, but there's a big lack of interest in the project.