Worth Reading: Do We Need Network Automation
A long, long time ago, Mircea Ulinic (the author of Salt networking modules) wrote a long and thoughtful blog post on whether we need network automation (TL&DR spoiler: yes).
After reading the article, you might want to listen to the Salt and SaltStack podcast we did with Mircea a long while ago, and watch his presentation in Building Network Automation Solutions online course (also accessible with Expert Subscription).
Funny timing. Was thinking about it just earlier today, and came to conclusion that network automation in the sense of writing tools / playbooks to do it is a niche thing and is IMO unlikely to ever become mainstream.
There are and will always be pockets of success, but I don't think it will ever reach the scale of say CCIE program. Not saying there's no benefit to it. Just that the scale of these benefits and the costs of getting them are very unequally distributed.
Can't say I can point to specific reasons, it's more of a result of an observation of what's been happening over time.