Q.  Why is it that with most of the fares you list , you have to book thru Travelocity or Orbitz etc. and not for example on the United website.... The exception is Southwest, which you do link to.  By the way, thanks for having such a dreamy site.

A.  "Dreamy?"  Wow, now we're feeling all teen idol-ish here.  Thanks!
Now to answer your question.  You actually can book the fares we list on the airline's website if that makes you happier.  We refer you to sites such as Travelocity and Orbitz because they show you blocks of dates all at once.  It's a lot easier and quicker to find what the available dates and times are for a sale fare that way.  And it's a convenience for you not to have to enter one date at a time.   (We link to Southwest because they don't sell their fares on any other site and luckily they have a great "Shortcut to Low Fares" feature that shows you a month of fares on a single page.)