Most people seek security and companies do not wish to be recruiting every minute, often a bad fit leads to short stays. The recruitment process is a long and expensive one, especially where agencies are used to introduce the candidate, so companies seek to avoid that at where possible. The best response is to indicate that you expect to be with the company for a few years, noting that you would enjoy being part of any expansion, which will aid your personal development. If you can reassure an employer that you would be there for a reasonable time, you are more likely to be considered. Young women candidates tend to get this question more than men, because of the possibility of pregnancy later on, but that should not be a barrier to having a permanent job or be used in a bias way against them.