We're not trying to be clever, TBH. There are many excellent alternatives out there in the Rust world. Our choice of Rust is primarily a technical choice, and later we found out that it's also a fantastic community to be part of.
Most of us have our roots in the open source world, many (most?) of us learned coding because we were able to look at open source code, make changes to it, recompile and play with it.
We're trying to give back to the open source community and at the same time earn a living by asking the people who use Slint for proprietary apps (i.e. not giving back) to support us by purchasing a license.
Frankly, that's a fantastic use of the GPL. The idea that open source developers should bend over backwards to support the use case of people who can't be assed to give back to the open source community is ridiculous. If a company wants to make proprietary software off the back of open source developers, they can pay for a commercial license. Everyone else is free to use the GPL.
All other so-called "free" licenses are just a way for corporations to co-opt the open source software community.