[twobyfour]

1) awareness. I didn't even know that site existed

2) Chicken and egg problem / opportunity cost. Every additional site I post a job on costs me time in posting the job and making sure the formatting works on that site. (The latter is a non-trivial time-sink). A site that has only 30 jobs probably isn't getting enough traffic from job seekers to be worth my time and energy.

3) I have no particular interest in reaching a pool of candidates whose only outstanding characteristic is that they want to use Slack at work.

4) Saying we use Slack at work does little to nothing to differentiate my company from those with whom we're competing for talent. Really, it doesn't even differentiate us all that much from those who use NO chat software at work.