My estimate though is that proper use of BIM (not just design & engineering, but also accounting and time management... 5D) would save anywhere between 40-70% on their projects.
So, why isn't it happening? Because the construction industry is always the last industry to adopt new technologies. "If it ain't broke, don't fix it" is the mentality. Also, if you're 40-65 years old and been building forever, it's not so fun to listen to 25-30 year olds tell you what's what. But that's what needs to happen.
The older guys in firms don't listen (the ones that do save a bunch of money...), and so the young talented people leave for better industries like software engineering, where they are actually respected and valued.
We are started to see SOME private companies, like Suffolk, really adopting new stuff. The big guys like Turner and AECOM are trying to adopt, but like I said earlier, their technology infrastructure is a JOKE! Try writing BIM automation scripts when your network admin won't even let you have root access. What a sad, sad joke it is.