Unfortunately, there are still functions that Twitter serves that nothing else does. For breaking news, it’s still unmatched. For celebrities, influencers, politicians, journalists, etc there’s no other platform that has the same microblogging function with the user numbers and clout that Twitter does.
Until that changes, its still useful. It gets less and less useful, but as long as the site is up, allows users to post up to the minute updates and allows users to follow posters, there’s only so far it can fall without real competition.