I'd break this in two parts:
- the majority of devs I know do use a preprocessor, mostly SCSS (few use LESS, even fewer use PostCSS)
- many people don't use a framework off the shelf, preferring either bespoke CSS or a bespoke framework customised exactly to their needs.
People definitely still write plain CSS though; and I always recommend people learn CSS before a pre/post-processor as you need to know what's being sent down the pipe after compilation.