Twitter became like the group chat feature which people were aware of, the difference of the "group" was the whole world. Twitter though thought to be a mixture of the interfaces of blogging and social networking but later people understood it was neither of the two.
Twitter was in its own league, with every celebrity becoming a part of it, it became more of popularity network. Now a celebrity's popularity is also measured by the twitter followers they have.
It was about time, the intelligent or rather witty people saw a great market in this and captured the whole system. Earlier people liked the witty jokes and sarcasm by the unknown profiles ("eggs") but then people understood the marketing behind it. Now every second person is either promoting a seo site, a internet marketing site or any e-commerce site.
News channels and their editors are busy promoting their news articles, their videos or their review. If you have ever subscribed to any of them you know how many breaking news a day you are bombarded with in your timeline.
The new breed in this promotion game are the politicians who have got a very easy way to get into the people lives and tamper with their thoughts. Political parties are having a team of people who are busy creating favorable trends for their political parties, which recently led to chaos in twitter.
So now when people are visiting twitter, they are like, Is there any real person here ? Is there anyone with unbiased opinion ? The sad state is most of the time the answer is negative. So keep "follow" and "unfollow" till you find the right people.