I've worked on the interview questions of TurboTax for close to a decade. The reason we sometimes ask questions that specify gender, such as the son or daughter question, is very simple. We often have to ask follow up questions that refer back to a person mentioned in an earlier response, and it's much easier and feels more personal if those questions are framed using pronouns like he/she/his/hers/etc. If we keep using the child's name over and over, or resort to non-gender-specific pronouns like "they", then the language of the follow up questions starts to sound very unnatural, and possibly even confusing (is "they" referring to all my kids?).
Marketing never even entered our mind as a consideration. Even if it had, there are extraordinarily strict rules imposed on tax software companies by the Treasury Department to prevent tax data from being used for any purpose other than preparing the tax return. We wouldn't jeopardize a very successful and honest business by running afoul of Treasury rules. And even without those rules in place, our business model is based on charging a fair price to the customer, not luring people in with give-aways and then selling your data to third parties.
