The key is Public Safety. Licensing was proposed and became a law in all the US States.  There are different requirements per state as each state has its own challenges, geography and other 

factors that may not apply to other states.  But there is also an industrial exemption. And many graduates of Engineering are not electing to become licensed professional. While I strongly recommend that any graduate of Engineering program in the USA get licensed.  There are advantages for being licensed PE. As to enforcement its really state by state. I think Arizona should have collaborated with the unlicensed professional by having licensed professional review of the work with the engineer.

The key is Public Safety. Licensing was proposed and became a law in all the US States.  There are different requirements per state as each state has its own challenges, geography and other 

factors that may not apply to other states.  But there is also an industrial exemption. And many graduates of Engineering are not electing to become licensed professional. While I strongly recommend that any graduate of Engineering program in the USA get licensed.  There are advantages for being licensed PE. As to enforcement its really state by state. I think Arizona should have collaborated with the unlicensed professional by having licensed professional review of the work with the engineer.