All the other buttons are just variations on the defrost button
Your standard-issue microwave will likely have, in addition to "Time Cook," extra buttons like "Pasta," "Potato" (?), and "Cream Cheese" (??), but they're all a sham. I don’t care how many super-specific entrees your microwave claims it can perfectly heat -- "Salmon," "Breaded Chicken Cutlet on Roasted Beets With Goat Cheese" -- not a single one of your microwave's keys will activate microwave engineering that goes beyond the simple 0%-to-100% power mechanics explained above.
Because the options on your microwave are just part of a marketing ploy
According to Schiffman, it's all part of a consumer-targeted scheme. "Everyone’s trying to differentiate their oven. So they put more buttons and more functions. They're all trying to outdo one another."
A less cynical take on the same theory is that excessive microwave design is an attempt to help clueless 21st-century cooks. "One of the major concerns we hear when we talk to consumers is they don't know when things are done. So, this might be a way to take some of that guesswork out," he says.