When Kabuki was first emerging as a dance form, the stage was fairly basic. Izumo no Okuni often performed on the ground, and later, a square board with a long ramp. This ramp, or Hanamichi, remained, as the rest of the stage morphed several times. By the early to mid-18th-century, a series of trap doors, Seri, were added to an elevated stage. Scene changes originally occurred with a wheeled wagon, called the Hiki Dogu, which held pieces of one-dimensional scenery. Around the time the Seri were implemented, the Hiki Dogu was abandoned in favor of the Mawari Butai, an elaborate turntable in the center of the stage.
For more information about Kabuki stages, please visit this site.
Bunraku was developed as an easier means to tell the more fantastical stories. Kabuki actors are trained in a set role and maintain that role for the rest of their careers. Such as the Onnagata, which is the female impersonator, meant that these actors were trained in very specific movements, and wore restrictive clothing. They could not easily adapt to the more dangerous stunts, and thus, puppets were introduced. The Kabuki and Bunraku play equivalents usually only differ in how the action is carried out, often when death and murder are portrayed. Or when a supernatural being is introduced. Though, this became easier in the mid-19th-century, during the Meiji era, when "Chunori," a way to wire costumes so the actors could fly, was invented.
Later in the 18th-century, the Kuroko were added, as a way to shift scenery, along with the Mawari Butai. They were small performers dressed all in black, with their faces covered. The idea was that when they appeared, the backdrop would also be black, and they would blend in- giving an impression that the pieces were moving on their own.
Please visit this site for more resources about Bunraku.
This video depicts a modern interpretation and rehearsal of the Nembutsu Odori Shrine dance, which is what Okuni was said to be imitating. Instead of the flags and drums seen here, Okuni was known to use fans, lengths of silk, and at times, Samurai swords.
What about Bunraku, during this time, may have made it a more attractive art form in which to write plays? What developments during the Tokugawa and Meiji Eras changed Kabuki to compete with Bunraku, and develop those plays for its stage?