People stick with their legendaries due to the fact that bungie has repeatedly shown a lack of knowledge when it comes to creating powerful weapons worth the amount of effort required to obtain them. When the do make a weapon do the correct amount of damage, people love to use it. Honestly, when was the last time you used the rarest tier of primary weapon (exotic) in PvE? There are 0 elemental primaries in the game under the exotic category. This is COMPLETELY stupid. There is no incentive to use a primary exotic over say a Gjallarhorn, or an Icebreaker, because they don't do elemental damage, and are useless in end game activities for killing enemies at a relatively quick rate.