That's because it has a launch and multiple inversions to make up for it. Not to mention that it's a smooth ride which is shock considering most Vekoma coasters have a reputation for being rough. I'm of the opinion that coaster enthusiasts don't care about time or ride duration but what they care about the most are the elements that the coaster goes through, the smoothness of the track and if applicable, the restraints.
And here's a number to look at: 2,000. That's the number of feet in coaster track for 7DMT. No wonder it's so short.....