Why is new construction not more popular?

[Fillipe Silvas]

I think I have finally narrowed down my interest to multi family, buy and hold investing. I have been searching my area and found many more multi family units for sale than I imagined there would be. Along with looking at units for sale though, I have looked into lots that would allow me to build a multi unit home. I have ran numbers on what I believe would be a very good deal for a 4 or 5 unit and am wondering why this isn't more popular. Am I missing something? Just want to make sure there aren't some hidden costs to this that I may not be considering.