With modern software development there is a ton of boilerplate and focus on tooling (how many hours do we waste on IDEs or text editors), compilers, build tools... whatever.
With APL or K, you don't really have a lot of that. Once someone is proficient, they can do a ton with just a tiny amount of code. Aaron Hsu has a bunch of videos online and chats on HN (user arcfide I think) on the strengths of APL in general and how he built a compiler to run APL on the GPU and got it down to like a page of the alien glyphs. His point is that with APL you can eliminate huge amounts of things like helper functions and see the entire code at a more macro level. He literally uses windows notepad to code in as well, so a lot less time is wasted on learning/managing/configuring all the tools in the ecosystem.
Supposedly they've done some studies where people can be taught APL pretty easily if they go in with an open mind. I can code a bit in it after only playing with it a bit. The symbols are a LOT more intuitive than you think (a lot of effort went into making them make sense in representing the operations they do). The big problem is professional devs don't want to get locked into a niche technology or admit there are other ways to do things that don't involve Java-like hell. This is less of a problem with finance workers using Kdb+ (a very fast array database that you access with the k or q languages) that get paid $$$$$$$ to write stock ticker analysis software.
As a CTO, I'm not sure what the lessons are except keep code more reasonable. Don't write stuff you don't need...etc. I'm guessing OP has gotten use to the expressive power of APL and the interactive nature of the software and how to keep things lightweight and now sees a lot of modern software as being overly bloated. It reminds me of a vendor that shipped us what should have been a page long application (pretty simple data transformations), but instead it was like 50 class files and all sorts of other junk. I was blown away by the inefficiency and extreme complexity for what we later wrote ourselves in a short script with few functions. Assuming it wasn't outright on purpose, I think certain industry tools encourage over architecture.