Myself, I think that's because the visuals pull you out of the film because they are so obviously bad (not even just in terms of the drop in quality from TMP but because they are actually I think just plain old bad effects work which should never have been allowed passed to begin with) and I think the one thing that a film can't always get past is if there is something within it that continually prevents the viewer from getting immersed into the environment of the story.
Could be cheap visuals, could be the script, could be a performance, makeup (to which, one can add Catwoman in the Nimbus III salon as well!) or whatever.
They become a distraction from some of the things that perhaps the story has to offer (which in TFF itself seems to be the movie franchise's second attempt to 'touch' God in some sense although this time in the more literal sense than in TMP), assuming that there are things to which some people could find mileage. Obviously there are because that is the case in almost every film.
'If the Apocalypse starts, beep me!' - Buffy Summers
'The sky's the limit.....' Jean-Luc Picard, 'All Good Things'
courtesy of Saquist