Because people would go through all the content in a few days and then complain about the lack of content for the rest of the season/year. It happened constantly in D1. Super hardcore players make up a very vocal minority.

Because used to they didn't, and everyone blew through all of the content in a week, then complained that there's nothing to do until the next DLC because they spent 16hrs a day grinding through all of the content.

Luke

Well there are kinda two camps, neither of which are exactly wrong. Camp one says gimme everything but then people will complain about content drought (see D1 dlc). Camp two will say give us stuff to do weekly so there's no drought but people who want to grind the game pretty hardcore run out of stuff to do weekly and complain about it. Either way you look at it, it's a tough and great place for Bungie to be in. I think Aztecross said it best in one of his videos a ways back: Bungie has created a game where people just want to play the piss out of it. Honestly it kinda makes you wonder if Bungie blew up the Destiny team even more than they already are and upped the season pass cost proportionately with more content if that'd float.

Because they can’t make quality content in high enough quantities to satisfy the player base. Also, the elements of the game are too shallow so they have to drag it out over time.