Since questions have been moved to the subdomains users gain money from the ads placed around the questions. So you make money by asking questions that are interesting to the community.
Questions are also able to be found by google so someone asking the same question as you would theoretically find it and easily get the information they needed... while viewing the ad and making you money.
You can easily ask poll sorts of questions or ask for opinions about topics. Things you can't exactly search on google