Their real value prop is being able to provide cover for execs. They can act (emphasis on the word act) as a neutral third party who can lend credibility to an idea, and also become a scapegoat if it fails.
I've seen consultants hired for projects where everyone on the team (including leadership) basically knew what to do or what needed to be done, but they were only, say 75% certain about it. In a normal startup, they would've just done it, failed fast, moved on. But in a bigger corporate (non-startup) environment where they didn't know if their jobs would be on the line for taking risks, they could bring in consultants to verify but mostly echo back what they already wanted to do. Plus they come with certificates and stuff so everyone in the chain assumes that's worth something.
I've seen consultants hired for projects where everyone on the team (including leadership) basically knew what to do or what needed to be done, but they were only, say 75% certain about it. In a normal startup, they would've just done it, failed fast, moved on. But in a bigger corporate (non-startup) environment where they didn't know if their jobs would be on the line for taking risks, they could bring in consultants to verify but mostly echo back what they already wanted to do. Plus they come with certificates and stuff so everyone in the chain assumes that's worth something.