It's used pretty often. It's not slang, but it IS informal. It's one of those phrases that suddenly became popular a couple of decades ago and will probably fade in a couple of decades.
"It's all about X" means that X is so important, it's almost the only thing that matters.
In a clothing store, my wife was with me. The salesperson was showing me chinos and corduroy pants. I said I wanted corduroy, a very comfortable fabric. The salesperson said to my wife, "it's all about comfort with him, isn't it?" Meaning that I cared entirely about comfort and not at all about style.
In a news story, Texas cattle ranchers told reporters that in the extreme heat, "it's all about the hay." They meant that a good supply of hay was extremely important to the survival of the herd.
"Why do you keep going to that steak house? It's crowded, it's noisy, and it's expensive." "It's all about the steak." That means steaks are so good they are more important than the atmosphere.