Many alternatives exist but none reach critical mass because twitter has buy in from the major media outlets and the journalists they employ. Unlike other social networks that grew spontaneously, Twitter was effectively crowned.
Every twitter clone that tries to compete without first having the approval of the major media outlets will either be publicly ignored, belittled, or outright attacked.
Every twitter clone that tries to compete without first having the approval of the major media outlets will either be publicly ignored, belittled, or outright attacked.