I often see people praising Twitter for its usefulness, coolness and relevance – ironically mostly on Twitter itself. In the context of science, for example, Twitter can make conferences more enjoyable and interactive, allows for self-promotion and is an excellent tool to stay updated about recent publications and developments (e.g., here). Although I am not very familiar with the marketing and journalism communities, I imagine Twitter is one of the favorite – if not THE favorite – social media platforms for similar reasons. Also the tech community and celebrities belong to the most avid Twitter users.
All these communities have one thing in common: They are highly educated professional elites that by the very nature of their job must communicate with as many interested people as possible. They (should) have something to tell and sell. They want to be heard. Or putting it the other way round, they are not the average person who lacks the ambition to reach beyond existing circles, such as family and friends. Consequently, the average Internet user (think about your mum, dad, uncle or friends from primary school) does not see the point in Twitter. S/he doesn’t get its lingo and conventions, either (“retweet? mentions? 140 character limit? hashtag? lists? abbreviations? WTF??? why would anyone want to do that??”). Facebook, by contrast, caters to almost everyone because it offers more functionality and serves our basic interest for what’s happening in our wider circle of friends and acquaintances. It’s probably easier to understand for the novice user than Twitter as well. On Facebook, the people that “have nothing to say” can still observe what’s going on, they can chat with their friends, participate in events and express their preferences via likes in a relatively closed environment (at least in their perception, whereas Twitter is mostly used in the public mode and thus accessible by everyone).
I think these basic differences in the perception can partly explain why Twitter struggles to increase their user base (http://www.wired.com/2015/07/twitter-problem-users-still-dont-get/) – despite mainstream media “promoting” Twitter to lay audiences, for example by showing tweets after sport events on TV or compiling Storifys.