Why do keyboards use QWERTY?
The short answer
QWERTY spread through nineteenth-century typewriters. As more people learned it and more machines supported it, computers inherited the layout even though modern keyboards do not have the same mechanical jamming problem.
How it became established
Typewriters developed by Christopher Latham Sholes and others, followed by Remington products and training, helped QWERTY reach a wide audience. Once many users knew the layout, schools and offices benefited from keeping the same arrangement.
Is its origin completely settled?
The famous explanation says the arrangement helped avoid typebar collisions. Other research connects parts of its development to telegraph operators. The details remain debated, but widespread adoption and familiarity clearly helped make QWERTY a standard.