Sepia was extremely popular in photography prior to 1930 for two main reasons. The first reason is more logistical. The chemical toning process and the sulfide compound it creates is more protective than the traditional metallic silver found in black and white processing.
This is the reason why some of the oldest existing photographs are in sepia. Sepia photographs last between 50%-100% longer than traditional black and white photos.
Sepia tone photo taken in England in 1895
The second reason the tone was popular was because of the warmer colors it created. Artists and photographers saw value in the warmer tones of sepia photographs because it was different than the typical black and white tones found in the rest of photography.
In the modern age, photographers use sepia toning or digital editing to replicate the look of older, historical photographs. Sepia tone can add a layer of nostalgia that can help tell the story of a photograph.