In my experience they use it as self-imposed punishment to motivate them to actually work. even if they set up some deadline that only they know, the cost of not meeting that deadline is wholly insignificant compared to a publich deadline; forcing them to actually work instead of just endlessly push back private deadline and drastically increase time to deploy projects.
Once you stop thinking that these types of devs optimize for negative community reaction, their actual motivations make a lot of sense. A more responsible dev could 100% have publish deadlines, just stated with huge time lags to how long they estimate it could actually take. Any dev who consitatnly misses self-imposed public deadlines just uses the community reaction to motivate them to work. thats my theory at least.