Hair color products without ammonia were created because some people are sensitive to the odors of ammonia-based colors or experience skin irritation caused by ammonia. Ammonia-free products are often as effective as an ammonia based formula, but there are many clients whose hair is resistant to color and need the push from an ammonia formula to get it where it needs to stay.
I remind my clients that ammonia is used as an alkalizing agent, it opens the cuticle layer of the hair and this allows the color to really sink in. No-ammonia color uses weaker alkalizing agents to open the cuticle. If the cuticle is tight, such as often occurs when the hair turns gray, ammonia works better to open the hair shaft. I prefer it because the coloring results are far more consistent. Regardless of what you prefer, I wouldn’t be concerned about changing trends, they’re still safe and the manufacturer will still make it.