Why?
German deaf handball players using sign language in a time-out
Source https://www.handball-world.news/en/news-2-1-1-94866.html
Unlike the athletes in other IOC-sanctioned events (the Olympics, the Paralympics, and the Special Olympics), athletes cannot be guided by sounds (such as starting pistols, bullhorn commands or referee whistles).
The Deaflympics are further distinguished from all other IOC-sanctioned games by the fact that they are organized and run exclusively by members of the community they serve. Only deaf people are eligible to serve on the ICSD board and executive bodies.
The Games allowed Deaf people to compete in sports internationally. At the same time, it allowed young Deaf people from all over the world to meet, to learn from each other, and to experience a situation in which all are equal.