Because productivity was practically constant for this 99.9% of human history. Therefore the monetary base could be practically constant, too. With the industrial revolution, growth became obviously exponential.
Have a look at the following graph (nominal GDP):
http://3.bp.blogspot.com/_VO-2HbQsbSU/S9BbLF6MxBI/AAAAAAAAAR...
Or this one (real gdp):
https://ourworldindata.org/uploads/2013/11/GDP-per-capita-in...
Inflation means the value of money stays coupled to the changes in GDP, just as in the millenia you apparently value for exactly this constant money <> gdp relationship.
Mankind came to what it is 99.999% of time without antibiotics too.
Arguments like this are rarely constructive.
It makes sense, really. Why should finding a old penny under the floorboards, nearly worthless when it was minted, make you rich?
I think that's what the child poster meant by bug. It's artificial and still: Why?
Mankind came to what it is 99.9% of time without artificial devaluation.