The simplest answer is "I don't know!", but here is some analysis.

VS Code is the one of the best free and open-source editor available that can compete with most of the paid editors and IDEs,
It has a huge community and extension support, if you're thinking about some feature, just search for it in the extensions, most probably which will be there. And VS Code is very much customisable, light weight, simple to use,

I am a huge fan of VS Code.

Then why WebStorm?

How I came to WebStorm?

I read about WebStorm, I did a trial, didn't like WebStorm, came back to VS Code, again read about WebStorm, no change back to VS Code, I did this multiple time,

When I had to work with large projects with lots and lots of files, felt something is missing in VS Code. At that time, I realised, how WebStorm is better than VS Code.

These are some of the point I came up to choose WebStorm over VS Code.

• It's an IDE, so it has most of the basic features built into it, no need of extra extension, so that most of the features works seamlessly.
• Much better performance with large projects.
• Much better refactoring.
• Even if it's an IDE, simple and cleaner UI.
• Built in support for most of the common front-end frameworks.
• Better support for version control system like git.
• Better intellisense

If you're working on large projects and you can spare the money for WebStorm, just go for it.