Not sure that Twitter is dying. I believe it is evolving. I believe social media is driving evolution in human interaction. Nothing startling or new in that statement. It is a modern truth. Another simple truth is that your perception of social media is entwined with the quality of those people and accounts you follow. If you notice change it could be that those you follow are moving into different virtual sub groups that you have not discovered yet (and a prolonged absence from Twitter is bound to highlight this).
Online nastiness, trolling and bullying is fixed with the block button. In real life blocking someone can be rude and unfriendly. In our online virtual lives it is simple, easy and goes unnoticed by the person blocked, generally (and if it doesn’t go unnoticed, you won’t know it in any case). What a blessing that is.