Mastodon isn't a Twitter clone but it was made to fill that exact niche. Short posts with mentions, hashtags, and URLs. Such details give the feel of a platform. The velocity, the atmosphere. On a personal level that's just what I like. And I think it would be reasonable to assume many of those who signed up do, too.
A social network is also a kind of common playground. Individuals have the capacity to spoil it for others. For example, when there was a bug in Mastodon that allowed you to make links spin, many made use of it for fun, which spoiled the experience for people with motion sickness. The more vectors there are for how information is transmitted, the more pronounced this is.
Server run by the main developers of the project It is not focused on any particular niche interest - everyone is welcome as long as you follow our code of conduct!