I think you're already getting at the "why", which for many situations you can view it as a leveraged investment. This site shows education as the biggest expenditure, and there's some argument about that resulting in an overall return on investment. If that is really the case then there's a large opportunity cost in not overspending.
The analysis is not always done sufficiently (or without bias) but that's the idea.
Sure but that's kinda my point. If they did this analsysis why isn't it blasted everywhere?
I've never seen a politician mention this kind of (we spend x for y returns) discussion or a doc on it holistically.
It's obvious to most people to invest money can give you more in return but that's not really discussed except peicemeal for one program at a time.