HATEOS can be a weighty concept to get across and it never clicked for me until I read a book on it. I still think there are aspects of it that could be learned easily enough in isolation though. Understanding media types for example allows you to develop some really nice schemes for API versioning. But few people are even willing to learn that and just butcher their URLs instead.
Thinking in terms of REST requires that you concern yourself about the full infrastructure. Many programmers i have met simply do not care. Super nice properties such as cacheable and discoverable are outside their domain. Most simply just want remote RPC.
Try convincing a programmer of the benefits of HATEOAS is though. It will be dismissed as too much hassle with no real benefit.
But if you look at it from a data architectural perspective everything just "clicks". Few projects are however approached from that angle.