Some new thinking is required to scale a jet engine to the size that it can be held in one hand. Some even newer thinking is required to go two orders of magnitude smaller. Some new thinking is required to build a nanojet engine that can be manufactured cheaply and efficiently. I believe there is an large market such engines at any of those scales. Not to mention the military.
Human beings love to employ the latest technology just for killing each other.
When Texas Instruments first debuted its digital chip for wristwatches in the 1970's they showed it to the Swiss watchmakers. There were 50,000 Swiss watchmakers at the time. None of whom were interested in silicon chips. Now there aren't 500 Swiss watchmakers. Change of paradigm.