I can't speak that much to why it failed overal, but it did have inefficient writing, lots of walls of text with little to say. But to me the number one cause the expansion and especially the sequel failed were because most players will want to finish the base game first before doing those. Making PoE2 a direct sequel with the same character was their major failing in my opinion. It might sell well, eventually, over time, as more and more players finish the first game. But they lose a ton of them because first of all the game needed so many patches to finally get to where it is now and most players will have it in the back of their mind to finish it some day but will just forget about it after a while.
I can tell you that the main reason I never finished the game, and the first part of the expansion especially is because it doesn't hold my interest. There was none of that world building and faction design that made New Vegas so compelling and replayable. The factions in defiance bay were so cookie cutter, there was lots of flair in the writing and presentation of the world but the content was linear and samey and it all blends together into one big bland soup as you play it. I can't even remember a single quest. Also RtWP is just a straight up bad idea and has been since it's invention. Maybe it can be done right but it's always been a compromise, a re-working of turn based to try to make it less "slow, boring, etc." and more appealing to the twitchy casuals. I mean, that's my personal opinion and preference but it's the correct one so. .
