I think there were several factors. While Tk (one of Tcl’s major killer apps) looked good on Windows and Mac, it retained the Motif look and feel for too long

I think there were several factors. While Tk (one of Tcl’s major killer apps) looked good on Windows and Mac, it retained the Motif look and feel for too long on UNIX platforms. This gave the impression of it being obsolete technology and made many people dismiss it for use in serious applications. It lacked a major company championing and investing in it. Its creator Dr. Ousterhout, moved onto other projects. Python, JavaScript, Ruby, and PHP won out on the scripting language popularity contest at the expense of Perl and Tcl. Richard Stallman had very strong opinions about Tcl that also did it no favors. This was known as the “Tcl War.” https://vanderburg.org/old_pages/Tcl/war/ https://vanderburg.org/old_pages/Tcl/war/