Why do developers struggle with social media marketing?
Short answer
Because the reflexes that make good engineering make bad posts. Engineers are trained toward precision, completeness and describing the system; social platforms reward compression, repetition and describing the outcome for one person. Posting feels like self-promotion rather than communication, and the accuracy instinct fights the compression the format demands.
The longer version
This question comes up inside a longer piece on the same problem. If the short answer above raised more questions than it settled, the full article has the reasoning behind it.
Every Way to Promote a Product, and Why Developers Get Each One Wrong