why do people buy html and css when they can go to the preview page and download for free

I don't get your post... who buys html and css?

@Cruiser why to buy templates (html & css) when you can click ctrl+s and download the script for free

@DavidKevork The HTML/CSS you see is often the rendered output from a CMS created using a mix of templates (php, blade, twig etc), static and dynamic CSS, static and dynamic JS, and some database content for defined settings and page content.

Copying the rendered HTML/CSS is next to useless unless it's a static website template you're looking at, or just want to copy the design superficially for your own 'reverse engineering' use.

For example, using a Wordpress default theme, the code that renders the HTML/CSS you see is generated by a bunch of php like this:
https://github.com/WordPress/...

When you buy one that includes full version and skeleton version in 5 6 major frameworks (mvc5 6, angular, meteor, react etc) you will understand.

It's called supporting the designers... If the template is good I buy it legitimately from themeforest...