"What You Leave Behind" actually has the highest IMDb rating of the Star Trek finales, sitting pretty at 8.7. "All Good Things" and "Endgame" are tied at 8.3.
The films have unrealistic ratings as well. Wrath of Khan is 7.7 while Abrams' Star Trek is 8. First Contact has a rating of 7.5. The other 11 have ratings in the 6 range.
There's also a fair amount of trolls on IMDB who like to vote lower scores on shows just to mind screw fans of those shows.