Where do people get the idea one resource is supposed to teach you a language? As someone who has learned and uses multiple foreign languages Rosetta stone, pim

Where do people get the idea one resource is supposed to teach you a language? As someone who has learned and uses multiple foreign languages Rosetta stone, pimsleur, duo linguo are all fantastic tools for their indended use cases but language requires reading, writing, listening(to natives), speaking and many other smaller skills. With just whats available on the internet and mail you could learn a language in a matter of years but so many people complain because 1 app didn’t teach them in 3 months what it took their entire life to learn in their native language.