Any number of reasons exist to turn a manual car automatic. The most obvious is lost mobility: Injury or illness can leave a driver unable to operate a clutch or a stick shift. For a person who still relies on their car for everyday activities, the best option may be to rebuild their ride from a stick shift to a gear selector?
If you have an older model vehicle, switching to an automatic transmission is more manageable because there will be fewer computerized systems and wires. An automatic transmission runs off a TCM or transmission control module that collects data from sensors in the engine, so it knows when to shift. This computer is missing from a manual transmission vehicle and would be one of the components needed to convert to an automatic. This is a complex process and requires a knowledgeable professional. That professional would also need to swap out the gearbox and clutch.