If you go into a particular topic (e.g. 'Travel') the default view is to show only 'Recent posts'. (In the case of 'Travel' that means that there are only 14 questions shown there at the moment, with the oldest being from 11 December).
However you can still see all the questions that have been asked within that topic since the early days of AB, simply by clicking on 'Answered' and/or 'Unanswered'. (Somewhat oddly, 'Answered' only goes back to 2006, while 'Unanswered' goes back to 2004 in 'Travel').