Why Does Bootstrap Require jQuery?

In hindsight it's easy to judge (as you are doing rather shortsightedly), but back in 2011 jQuery was not considered bloated or outdated and was the main proven library that offered easy DOM access. So in that context it made perfect sense to use jQuery.

In fact, 6 years later there may still not be another library with the same robustness and feature set of jQuery.

Jquery is a popular frame work and lots of developers have experience writing in it, making their documentation easier to digest. It's also very good at dealing with a lot of the cross browser quirks that javascript presents.

If you really don't want to use Jquery, there is bootstrap native: http://thednp.github.io/bootstrap.native/