We are using it for our apps, but I can see why people do not use it for new projects:
1. The state of C++ is not great. Few developers, C++ footguns, complicated build systems, and generally slow progress, see my https://arewemodulesyet.org/
2. How Qt presents and licenses itself. Either you go LGPL or you have to pay big money for a commercial license, which will then infect all other apps as well. For example, when you have two Qt apps that talk to each other you must license _both_ commercially.
3. The split of Widgets and QML makes the ecosystem fragmented, because Widgets will never die. Even the Qt devs themselves are split about this. You can see this when example code for a new feature uses Widgets. QtCreator is also a nice example, where they reverted some new QML code quite a while ago and have not substantially added any new QML code since then.
4. Tooling: We use QML for everything and the tooling is not great. The language server is still super flaky and breaks, and developer tooling like the Chrome Dev Tools is virtually nonexistent.
5. Packaging is still also not great but has gotten better in the last few versions where Qt creates a deployment cmake script for you, but you still need logic for your own (vcpkg) packages.
1. The state of C++ is not great. Few developers, C++ footguns, complicated build systems, and generally slow progress, see my https://arewemodulesyet.org/
2. How Qt presents and licenses itself. Either you go LGPL or you have to pay big money for a commercial license, which will then infect all other apps as well. For example, when you have two Qt apps that talk to each other you must license _both_ commercially.
3. The split of Widgets and QML makes the ecosystem fragmented, because Widgets will never die. Even the Qt devs themselves are split about this. You can see this when example code for a new feature uses Widgets. QtCreator is also a nice example, where they reverted some new QML code quite a while ago and have not substantially added any new QML code since then.
4. Tooling: We use QML for everything and the tooling is not great. The language server is still super flaky and breaks, and developer tooling like the Chrome Dev Tools is virtually nonexistent.
5. Packaging is still also not great but has gotten better in the last few versions where Qt creates a deployment cmake script for you, but you still need logic for your own (vcpkg) packages.