When Scott Fischer was stricken, his friend Anatoli Boukreev climbed up to him with oxygen. Same with Francys Arsentiev, her husband Sergei went back for her and died. On K2, Ger McDonnell attempted a solo rescue of three incapacitated Korean climbers. It isn't like there's a strike force of Reinhold Messner clones waiting at Base Camp ready to run up and pluck tourists off the mountain.
Edit: Hell, rescue below 7000m or 2000m isn't guaranteed. Back in 2009 one of my friends turned around on Aconagua just before the summit due to weather. During her descent she passed an ascending party. That group got disoriented and trapped by the storm. By the time rescuers reach them four days later two climbers were dead or dying.
theres a reason people are left for dead and walk back to camps in the middle of the night (beck weathers is the de facto example) and its because they are so incredibly competent and prepared that they are able to survive but at extreme costs to themselves and those around