Why nct dream is the most popular and successful nct unit?

I thought it should be nct 127 since they are more heavily promoted?

Stop

Dream and 127 are about at the same level success-wise.

And 127 isn't promoted better than dream, just look at what happened last year. Dream was supposed to go through a graduation process so that's why SM didn't put as much resources into them. But! Now that they are a permanent unit, they get as much attention as the other units, maybe even more.