This is by no means a "new thing"; everyone should have seen this coming once it was realized that you get esoterics/achievements just for doing the mission. If that's all that people care about, what makes you think they are going to stay there the entire 90 minutes?

if they are doing it for easy(and quick) esoterics then they are still screwing themselves over with the 2 hour cool down from the time you enter, so if you spend 30 mins on doing the objectives then you have to wait 90 before reentering (kind of quicker to do expert DR even as DPS)
1) cooldown is 45 minutes now, not 120
2) what makes you think diadem is all they are doing for esoterics?