CAD/CAM modeling software is resource intensive and users always complain about slow performance when manipulating big files so writing that type of app in Electron/Chrome/Javascript browser engine would be worse than native C++/Qt.
That said, another competitor Onshape is browser-based and yes, people do complain about its performance.
Some other well-known desktops using Qt are Autodesk Maya and Wolfram Mathematica.[2]