Why is estimating Constructon Cost & Controlling it Difficult?

[Vijay Kurhade]

Most uncertain or fluctuating price items as far as entire development goes are Land and Sale prices, but other areas remain fairly possible to estimate at very early stage in project.

Even then, Why does following areas are considered some of the challenges for novice to seasoned developers despite having so many tools nowadays to help them.

A] Estimating fairly accurate Construction Costs(Hard + Soft)

B] Controlling Costs, Budget

C] Financial structure (equity, debt, draws, taxation, insurance)

Thanking in advance