In the original Destiny, each weapon drop can have stats randomly assigned to it. With this approach, it means players were encouraged to grind missions over and over again for a chance to get a more powerful version of their favorite weapons.
However, in Destiny 2, this randomly assigned stats mechanic will be removed.
This random stat mechanic has been used in similar games for years - it's a system that's been used in Borderlands and Diablo, and it's been something that has fueled the addictive nature of these types of loot-focused games. With the random stats gone in Destiny 2, getting good gear is still rewarding, but once you've got the best weapons in the game, you'll know that there isn't a chance to get even better gear.
This has the potential to reduce the replayability of Destiny 2, especially if there isn't enough content added to the game. Destiny originally had very little content, but it was the chase for better loot that got players happily replaying the same content over and over.
There are two major reasons why Bungie has taken this new approach to loot. The first reason is so that those who don't have hours to grind each day still have a chance to get the best weapons. The second reason is for balancing - with every item type now having the same stats, it will be far easier to balance weapons, which is great for the Crucible.