Here’s just my opinion and I don’t mean to be abrasive towards anyone—but I’m not sure if it’s Free Code Camp’s, or anyone’s, fault that people are not shortening their URLs on Gitter.
In my opinion, the issue you have raised is no different to saying “it’s bugging me that people don’t line up at bus stops properly”, “it annoys me to no end that people don’t bother typing with perfect grammar”, or “why doesn’t anyone close down restaurants that make terrible food”.
It’s actually not ironic that the challenges exist and that most people who ask questions are not shortening links—many people, for good reasons, go through the FCC curriculum in the order that it is currently laid out but, if I’m not mistaken, the URL shortener challenge comes much later in the curriculum. In addition, and if I were allowed to hazard a guess, most people who ask questions are also not experienced coders, too.
If nothing else, the amount of time it takes to shorten a link and the additional amount of traffic that will be passed through the Internet to shorten a link is probably usually far greater than simply copy and pasting a long URL of an already-opened page.
I absolutely agree with your views in terms of readability and aesthetics, and I would do the same, too—but it’s most likely something that you simply can’t hope to enforce, particularly when it comes to the less experienced.
Alternatively, I suppose Gitter could automatically convert all links to bit.ly links since it’s a service that they are offering.