Exactly but there is so much more to Twitter that a directory would bring to light. Twitter brings people closer to brands and other people. The likelyhood of being contacted directly from customer servie or your favorite celeb is greater on Twitter than any other social media forum however most people don't realize this or use it to their advantage.
Cities are trying! In the last 3 years here in Kansas City I have seen a slow but steady change to make the city more bike friendly. But unfortunately it requires more than community interest. The streets here, especially in the city, are not conducive to bikes so it takes time to get the city to approve and implement the appropriate upgrades. But just a few weeks ago we got our first bike share system, Kansas City B Cycle. Change is a comin'!
Twitter currently takes new users through the process of selecting interests and suggesting who to follow but in my experience they don't do a great job. Even with the implementation of those suggested accounts, the discover tab and verified accounts, finding accounts to follow can be infuriating. A directory would make a huge impact as it gives user,new or old, an instinctive way to locate and discover better accounts.