It's a "random" guess. But in my experience, for a website, if it doesn't look good at first sight, a user might just leave instantly. As someone pointed out in the comments, just looking at sites like:

https://riverbankcomputing.com/software/pyqt/intro https://electronjs.org/

Your eye will probably be more attracted by the good design of the electron website.

I'm not saying an app should be only good looking, but it's clearly a major part.