But I have yet to see a beautiful TCL application. Web apps today can't just work, they have to be user-friendly and familiar to a wide audience. Would love to be proven wrong, but TCL does not seem to fit the bill.
I'm not necessarily advocating for that... but what on earth does anyone's choice of server-side framework have to do with the "user-friendliness" or "familiarity" of the client-side UX?
You can serve up a bleeding edge Vue.js app from a PHP backend, or you could serve up a bowl of jQuery spaghetti from Rust or whatever new language comes out next week. These matters can sometimes be tangentially related, but are largely orthogonal.
You SEEM to be referencing the "Tk" portion of Tcl/Tk. Tk is the desktop GUI framework that comes with most distributions of Tcl. But it has no apparent relevance to this or any other Tcl-based web framework.
This is kinda like dismissing a Java server-side web framework because Swing is ugly, or dismissing C# on the web because you don't like WPF.