It's not clear that nailguns are more complex than hammers. What is the measure of complexity? Nailguns are easier to use for a complete newbie, so a nailgun could be seen as a simpler tool. Becoming an expert hammer user takes literally years.
There are many different ways to measure complexity. Learning curve, interface, potential for virtuosity, amount of time implementation took, etc.
Nailguns are wayyyyy simpler to use than a hammer.
As a one-time (long ago) silver smith, I can tell you that while there were more than 30 hammers on the wall, there was not one nail-gun. A brief tour of books on subjects from book-binding to leather engraving should demonstrate that there is not a one-size fits all replacement for a tool whose many forms have been developed over centuries (if I handed you a hammer used by a roman carpenter, you would know a.) what it was and b.) how to use it) is just silly. Try making the last finishing cut with a carving tool using a nailgun before you say anything about simplicity...
There are many different ways to measure complexity. Learning curve, interface, potential for virtuosity, amount of time implementation took, etc.
Nailguns are wayyyyy simpler to use than a hammer.