In my experience, younger Millennials and Gen Z’s that vote Libertarian have the following characteristics:
1) White males
2) Reject socialism and many forms of government control
3) Are really concerned about government spending and the debt
4) Think both parties are corrupt & only care about big money
5) Are non-religious and are sick of the GOP’s social/cultural conservatism
6) Don’t like the Democrats plans to spend a bunch on social welfare stuff.
The most important of the 6, though, are #2, 4, and 5.
I think there is a certain generational aspect to some of this.
I'm a mid-Millennial (b. late '80s) and I think for a lot of people my age, libertarianism served the purpose that socialism or tankie LARPing seems to be serving for some disaffected Zoomers. It's an anti-establishment ideology that allows you to criticize the status quo without taking sides in contemporary political conflicts. This was especially true in the Bush years when conservatism was heavily defined by opposition to gay marriage and support for war in Afghanistan, Iraq and possibly Iran.
A lot of the people I knew who identified as libertarians in their late teens/early 20s simply drifted into the mainstreams of one of the major parties as they got older.
One of the most ironic and disturbing phenomena is how many college kids who were into Ron Paul in 2008 are now basically blood-and-soil Trumpists, and I think that says a lot about what libertarianism actually is as an ideology in practice in the United States.
