For me it's the storage. Lettuce goes bad, fruits rot, bread gets moldy, all within a short timeframe.
I buy some Soylent and it will be good there for a while. So when I'm hungry and we are out of bread, now it's a 30 second meal vs a 30 minutes or more to run to the store.
... Which as far as I or anyone else knows has nothing to do with it's shelf-life.
Regardless, I'm hoping you realize that I was being general and using "Soylent" as the example there because that was the topic of conversation.
Also your comment is especially funny to me as I've never purchased Soylent the product. I have things similar to it, but I've never bought any Soylent. Once they get this figured out, I might try their bars, but they seem a bit expensive for me which is why I'm always apprehensive to pull the trigger.
I buy some Soylent and it will be good there for a while. So when I'm hungry and we are out of bread, now it's a 30 second meal vs a 30 minutes or more to run to the store.