It's about knowing how to structure problems, whether the components are public or whether the problem space is completely unfamiliar.
E.g. someone who guesses "$3 billion" on only a gut feeling likely wouldn't be a strong hire even if the number is correct, while someone who can correctly decompose the final answer into its components and make reasonable estimates would be a much better candidate.
For estimation interview questions, and problem-solving questions more generally, a "structural" approach to breaking down problems is important because on the job the interviewee will need to be able to identify what levers are available to them.
E.g. someone who guesses "$3 billion" on only a gut feeling likely wouldn't be a strong hire even if the number is correct, while someone who can correctly decompose the final answer into its components and make reasonable estimates would be a much better candidate.
For estimation interview questions, and problem-solving questions more generally, a "structural" approach to breaking down problems is important because on the job the interviewee will need to be able to identify what levers are available to them.