Why are there so few private inspectors who can inspect construction projects?

[Matt A.]

Its typical for real estate investors to hire a private home/building inspectors to inspect a real estate property before they buy it. There are many licensed inspectors you can hire to do this. 

However, why are there barely any private inspectors who can be hired to inspect construction/remodeling projects being done on properties? 
I assumed having such inspections done during construction/remodeling projects was standard. I'm amazed to find out it is rarely done.  

Or perhaps there is a world of inspectors who do this and I just don't know where to look?
I''ve only heard of ones existing who work on large constructions projects, not small single family home investment properties.