History: The light pen is a unique antecedent, as it is a first attempt at touchscreen technology. It is a
“penlike input device that was used with cathode-ray tube display to point at items on the screen or to draw new items or modify existing ones. The light pen had a photosensor at the tip that responded to the peak illumination that occurred when the cathode-ray tube scanning spot passed its point of focus. The display system correlated the timing of the pulse from the photosensor with the item being displayed to determine the position of the light pen.”
The light pen had its beginnings in MIT’s Project Whirlwind in 1945, the project that built the first real-time computer, when they created the light gun as a computer interface system. The project was shut down in the 1950s, but experimenting with the light gun was continued by others, which allowed for the light pen to improve.  It competed with the mouse in the 1960s and 1970s, but was eventually phased out.
Why it was not picked: The light pen was not picked because it was not user-friendly. In an experiment run by Doug Engelbart, Bill English and Melvyn Berman on computer input devices, the light pen did not get good results. Subjects found that they had to reposition mounting of the pen after each selection. 
- John Daintith and Edmund Wright, “light pen” In A Dictionary of Computing: Oxford University Press, 2008. Accessed April 23, 2017. http://www.oxfordreference.com.ezproxy.umw.edu/view/10.1093/acref/9780199234004.001.0001/acref-9780199234004-e-2761
- John Daintith and Edmund Wright, “Whirlwind” In A Dictionary of Computing: Oxford University Press, 2008. Accessed April 23, 2017. http://www.oxfordreference.com.ezproxy.umw.edu/view/10.1093/acref/9780199234004.001.0001/acref-9780199234004-e-5809?rskey=YSJWe7&result=6230.
- Axel Roch, “Fire-Control and Human-Computer Interaction: Towards a History of the Computer Mouse (1940-1965).”, Lab. Jahrbuch der Kunsthochschule für Medien in Köln, August 28, 1998. Accessed February 20, 2017. http://web.stanford.edu/dept/SUL/library/prod//siliconbase/wip/control.html.
- William K. English, Douglas C, Englebart, and Melvyn L. Berman. “Display-Selection Techniques for Text Manipulation.” IEEE Transaction on Human Factors in Electronics 8, no. 1 (March 1967): 13.