The question is asked to owners. Renters are asked how much they actually paid in rent. The main reason why owners are asked for their estimate is because owner-occupied houses can be systematically different (probably more expensive/higher class) than renter-occpied houses, so estimating owner-occupoed rents with actual rents can be biased.
That’s a very poor proxy for housing cost."
Agreed. Rental data is publicly available. Why bother asking only to get a worse answer?