Because it costs more than other dvd media and cannot be played in most (all?) dvd players.
For data, it is the best and only format for general use as its reliable, does last for many re-writes, and so is best for backup of media you wish to amend.
It is not ideal for one-time recording as per it’s cost and incompatability in players.
It is not dead - so why the ‘dissapear’ in your post - you can get the media most places I know of - maybe not general high-street retailers - but they only cater for numb-nut joe-public who are taken in by salesmen, promo’s and advertising bullshit.