I have been using prepros for a while. It's a easy to use precompiler that pretty much does everything I need. I heard it is not good for team work but didn't know why. Why would you spend time to set up gulp to for minification, concatenation, uglify/mangle, live reload and live server when you can simply press one button and do all of these works in 5 secs?
I've never used Prepros and therefore have nothing negative to say about it. However, I think:
a) Your point is somewhat reductionist. Gulp isn't just a precompiler, it's a task runner and can likely do a lot more than what Prepros is able to do out of the box. It's great if Prepros fits your needs, but what happens when you run into something that it can't do? b) Gulp/Grunt/etc. are free (limiting proprietary software purchases is often beneficial in a team setting) and open source (easily tailorable to your needs)
As an aside, I'm not sure if Prepros allows settings to be shared by different members of the development team, but will gulp/grunt/etc. you check your gulpfile/gruntfile/etc. into source control and build tasks/etc. are available to all developers with access to said repository/project