Using an ascender on fixed ropes clarification

I want to get some clarification regarding using an ascender on fixed ropes. All of the rock climbing tutorials I’ve seen using an ascender have a secondary backup of a second ascender, Grigi, prusik etc. However, every video I’ve watched from people going up fixed ropes in the Himalayas seem to only have a single ascender. Am I just not seeing backups in these videos? Are these people accepting the risk of only have a single ascender for speed sake? Or just ignorant that they should have a back up? Would like to hear from some people with experience on fixed ropes.