Many Software Engineers haven't internalized this concept of time value. A lawyer or a doctor would never do real work for free as part of an interview process but for some reason we don't see it that way when it's about writing code.
interesting observation! makes sense. i wonder if it's because engineers are generally salaried instead of billed hourly. given all the 'crunch' and unpaid overtime, we'd be a lot more expensive hourly - folks might realize their real value. instead we give free overtime and then extend that into free interview time