That is true, but web-design and web-development are pretty close to each other and I'm pretty sure there is a lot of people out there doing both.

There is also counter-examples: KiCad is an EDA tool which is very, very close to the commercial ones.

But it's a great point, we could look at the counter-examples - good Open Source tools not aimed at developers - to maybe find out why they exist and how to do it.

Browsers come to mind, Android in some regards. But hopefully we can find something else than ad-delivery infrastructure.