To put the question a bit more nicely than my sibling, don't Tk apps all look... really bad? I don't know if I've ever seen a Tk app that tried to mimic native widgets at all.

For example, the most prominent Tk application I'm aware of looks like this on Windows: https://upload.wikimedia.org/wikipedia/commons/2/2b/Scid_4.6... On Linux (where I use it), it looks even worse.

While Qt doesn't use real native widgets on all platforms (IIRC), it at least seems to effectively mimic them under most conditions.

Last time I checked (years ago), apps using ttk widgets (rather than old tk widgets) look nearly native on Windows, but still ugly on Linux (matching neither GTK nor Qt themes).

ttk (which was introduced in tcl 8.4, circa 2002) uses native widgets on Windows and Mac. The default theme on linux is ugly, but there are reasonable themes available.

There was an attempt at a GTK backend for ttk on linux, but apparently there were technical difficulties so it was abandoned.

Tk also looks like ass in today's environment of ｍｏｄｅｒｎ apps with their abundance of white space and dearth of affordance. Your Windows 9x-like Tk app will stick out like a sore thumb.