Future.Travel works with more than 275 airlines to provide ticketing options. Some airlines do not like online travel agencies. Some carriers have restricted sale of seats only to their 'preferred buddy' travel agents.The travel market is very competitive and so there is sometimes a turf war on who get's access to tickets. The main problems for free access to ticketing 'equality' comes from national 'flag' carriers.
In some cases you may not see your preferred airline as they have not provided the lowest fare for the route (and more than 100 other booking options exist). You may force the Future.Travel site to search for your preferred carrier by using the advanced search options on the search page.