Because you should be able to use whichever types of events you want in your code, and also to ease transition of old products on to new platforms without rewriting code.
Include touchpolyfill.js or touchpolyfill.min.js on your page and keep using touch events.
You can view a functional demo of the touch polyfill at: demo
People Using Touch Polyfill
Do you have a project using touchpolyfill? Let us know and we'll get you on the list!
Please let us know if you're having any issues with this project -- we're looking to make the web a better place so we need testers and bug reports.