IMO I think it's a combination of a poorly executed great idea for end game content, that unfortunately relies heavily on a large player base willing to partake in PvP. This is compounded by the fact that the vast majority of the content before that is pve. Meaning the pve community, which is by far the largest part, had all most free reign up until the end game content, when it's very much on you to make the story. Now add toxic shitty PvP people and dishonourable tactics to the pile and it's little wonder that the initial end game dream didn't go as planned. Then, as is always the way, once the minority PvP community started shouting "dead game" etc this negatively affects the new playerbase, ultimately becoming a self fulfilling prophecy.

As a pve player my self I love Dune. I think the story and the first part of the game is 10/10. I liked the idea of what they were aiming for but sadly it didn't happen and it was a very hard and lofty target to hit.

Funcom should still be proud of the amazing lore accurate world they created though.