Why don't astronauts go outside?

A spacewalk isn't improvised. The crew spends days preparing tools and rehearsing the sequence, and on the day of the walk itself they spend hours pre-breathing pure oxygen to purge nitrogen from the blood: the suit operates at a much lower pressure than the cabin, and without that purge they'd risk decompression sickness just like divers. Then comes suiting up with help, depressurizing the airlock, and, on return, the entire process in reverse plus inspecting and drying the suit. A seven-hour spacewalk can consume half a crew's working time for a week.

Outside the module's shielding, the body is separated from the vacuum by a few layers of fabric and a visor. Radiation exposure rises, micrometeoroids are a constant threat, and a failure in the cooling system or oxygen supply leaves little margin for error. There have already been serious scares, such as the water leak inside a helmet that forced a spacewalk to be aborted in 2013. That's why the rule is clear: if a task can be done from inside or with the robotic arm, that's how it's done.

Spacewalks are reserved for repairs no machine can carry out: replacing ammonia pumps, installing new solar arrays, swapping batteries, or routing cables for newly docked modules. In those cases the advantage of human hands outweighs the risk. The International Space Station schedules only a handful each year, and each one is rehearsed beforehand on the ground, submerged in the huge pool at Houston's Neutral Buoyancy Laboratory.