Tcl/Tk is cool. Tcl/Tk makes UI's that jar in an ugly, immediately recognisable as "old-fashioned" way. This matters to users whether we like it or not. It would be a very niche commercial software project that used it for its UI no matter how beautifully elegant the functionality of its UI. Best ever UI will still elicit an "Ew, yuk." From the majority of its users. Graphical UIs have been de rigeur for what, 30+ ye…
It's also really easy to create truly ugly (but functional) GUIs in Tcl/Tk.