The home inspectors are looking for things that may come back and bite them, things that they may get sued over, likely relating to the later personal safety of the buyer. But they don't want to kill the deal.
Drainage problems costing thousands to fix is probably not on his/her list.
Septic tanks affect the health of the buyer so this may be flagged, but the burden of proof for the cause of the buyer's health problems may be on the buyer.
Roofs & foundations? Dunno'.
My inspector left me a list of questions to ask the seller before buying, stuff like "Has the central air and heating ever not been able to maintain temps between limit X and limit Y?".
My realtor was outraged and asked where I got these questions. I told her it was from the same home inspector that she recommended.
I still have those pages of questions somewhere.
The worst home buyer ever would be a person who is a structural engineer, plumber, electrician, carpenter, HVAC tech and attorney.