To expand, in contrast to other historical eras in Japanese history. I mean, it seems like a huge proportion of Japanese novels/movies are set in this time, and when you think historical drama in Japan, Sengoku Jidai seems like the go to era, in a way like China and the Three Kingdoms.
The reason behind the popularity of the Sengoku-jidai in Japanese popular culture is the same reason why the Three Kingdoms is so popular in Chinese popular culture, namely there are a lot of heroes - Oda Nobunaga, Toyotomi Hideyoshi, Tokugawa Ieyasu, Uesugi Kenshin, Takeda Shingen; tragic figures - Takeda Katsuyori, Asai Nagamasa; and great exploits - Battle of Okehazama, Battle of Nagashino, the Hongan-ji Incident. As such, it was very easy to romanticize these figures and events and create great works of literature and art.
Another reason has to do with the extreme popularity of The Romance of the Three Kingdoms in Japan, especially during the Edo Period where the educated elite consumed a lot of Chinese literature. The Sengoku-jidai is the closest thing Japan has to the Three Kingdoms, which makes it easy to relate to. For example, Yoshikawa Eiji's Taiko (a great novel) is a romanticized account of Hideyoshi's rise that draws a lot of inspiration from the Three Kingdoms.