If the person is actually smart in a field, they probably have jobs in that field. A job that is often extremely mentally or physically involved, leaving little time for revisiting that job over recreational periods (no time to hang out arguing with strangers, life's tough enough). There might also be NDAs involved, or concerns from higher-ups that the user might post anything that might embarrass the company, etc. It is also completely common for the smartest people in a field to have not an inkling on how to set up a website or join social media (because they are generally... on the older side).

The result is that Reddit, and social media, are mostly people who have studied those fields and didn't get in. The results are self-evident.