Why do most interfaces rely on sticky top bars instead of sidebars?

Most web interfaces have the classic sticky topbar + 2-3 columns layout (just like StackExchange).

Some but few websites use a different approach and, instead, have a collapsable sidebar (i.e. BitBucket):

While the first approach is surely the most familiar one to pretty much everyone who's ever used the Internet (including the 50+ generation) and I can imagine it will work better for them just because they're familiar with it, I don't quite understand why sticky top bars have become the Times New Roman of layouts and are almost a standard for any modern UI.

Sidebars allow you to:

• save vertical space, which is limited (compared to horizontal)
• have a more responsive/consistent UI (and more easily achievable)
• can show you more content and be more readable (top bars tend to be thin to save more space)

so it feels like they should be preferred over top bars.

Do you know of any studies on this and what do you think it's best?