They're probably serving their existing customers well, since they're still around, but I doubt they're getting many new customers (or mass adoption) with these prices: http://www.lispworks.com/buy/prices-2c.html, https://franz.com/products/packages/.
See for example the price for VA Smalltalk...: $6995 for a new developer license.
https://www.instantiations.com/products/purchase.html
Or VisualWorks, which charges based on either end users, number of CPUs, or a royalty basis.
It's a special niche market and in the Lisp space there are unfortunately no companies left of those which once sold actively maintained mid-priced Lisp systems with actual GUI Libs/IDEs (Dead/sold/abandoned/unmaintained: Procyon CL, Expertelligence ExperLisp, Corman CL, Digitool's MCL, Golden Common Lisp from Gold Hill, ...).
The remaining ones are two of the higher-priced vendors: Allegro CL and LispWorks. There were attempts to offer commercial CL systems - but none with emphasis on GUI (example Scieneer CL).
My work was interrupted because my employer decided to scrap the project this was planned for. I've got permission to release it as open source, which I'll do ASAP (I'm in the middle of cleaning it up a bit). Incidentally my position was made redundant at the same time, so I'm currently looking for new work, most likely I won't have too much time to work on that in the near future, but I'll try to continue working it on the side and will be happy to help where I can. Send me mail to ch@christianjaeger.ch if you'd like to be notified once it's up.
Why? Racket is very far from only being a language research platform, it's also a very good general purpose programming languages, and its GUI framework is quite easy to use. I would give it a try if I were you :).
And for Common Lisp, there is of course LTk, it is extremely portable, but you have to live with the Tk UI toolkit (which got a pretty native look in the meantime).
Qt on the other hand is well documented, and reasonably stable over the years.
Its not about being supported or not. It's just an external. it's not up-to-date with java 11 https://openjfx.io/
You can also use clojure with it if you want a lisp dialect.
Does this come packed with most platforms (Mac, Linux, Windows)?
There are also Qt bindings for a bunch of other languages, but Python seems to be the best supported after C++