They became marketable during a time when adulthood was synonymous with being in a nuclear family with a full time wife who cooks. Pretty much from their inception they were looked down on as lesser meals and mainly only used when people's schedules don't allow for prep time and cleanup. You often see them depicted in media as a meal turned to when people are unwel or working under duress. Like you said, they're more expensive than just cooking but under late stage capitalism we're pressed for time.

However the last fifteen years have seen a new commercial niche exactly for the thing you're describing. My roommate in college had meals delivered to him with a subscription service that his parents paid for. His mother saw to it he went into his early twenties never knowing how to cook for himself, stock a pantry, or even really clean. These services have grown as an industry, you see ads for them everywhere now. Yeah there's a lot of people who don't know how to cook.