It's cross platform almost out of the box.

You rely on Chromium which is battle-tested and have frequent updates

You can hire web developers to sketch, prototype, deliver your GUI. You can connect it to your own website.

You can let your users creates plugins and scripts more easily with web technologies.

You already have most of the codebase if you want to run a Light version of your software online as a SaaS or free app.

> You rely on Chromium which is battle-tested and have frequent updates

Chromium has been battle-tested and was wounded severely. Embedding it in your application will not automatically add the regular security patches to it.

The ease of providing a styled user interface. In the 2000s, this was something everybody wanted to archive, the term for it was "rich user interface". Already back then, embedding a HTML widget seemed an easy way to archive that.

Qt has been supporting CSS-like styling of your native applications for quite a while now.

It's pretty hard and has a lot of problems. It's definitely not as easy as css and doesn't have as many options for styling. Sometimes, when you change one property, 5 other unrelated properties will change as well, and you need to manually set them. CSS is much easier to get a consistent theme for an application.

Ironically one of the big complaints against Java was that it didn't look native. Then not looking native became a feature.