The biggest mistake the average member of a frequent flyer program makes when it comes to using their miles for travel is believing that you just go to your airline’s website, enter the city you’re traveling from and where you want to go, and the website will spit out your options.
It’s also a perfectly reasonable expectation in 2017, but it’s not how it works. Different airlines do better and worse jobs at this, of course. Some don’t have all their partners online. Some won’t show all possible combinations of flights.