Twitter is very noisy. Your feed is filled with links to blog posts, news articles, videos and other content that takes you away from Twitter"s app/site. That makes it much more difficult to get your followers to see your content and engage with instagramt has a more engagement on the specific platform
Twitter is a way that younger users keep up woth news. Not many people use Facebook anymore so the people are chaning to Twitter. Twitter may be noisy but thier is always something to new to see and discover.