How did Johnson get the Libertarian nomination? What happened to the real Libertarians?
Many libertarians wanted to "grow the party" and rack up more votes than previous candidates did. Nominating candidates who had actually held office and run something looked like a good way to do that.
Plus, have you seen the other candidates? John McAfee, an eccentric inventor who lives in Belize or Guatemala and has had brushes with the law. Austin Peterson, a libertarian publisher. And a lot of other unknowns.
None of them would be mentioned in the polls or have even a glimmering of a shot at getting into the debates. The temptation of finally eating at the grownups' table was too strong for LP members to resist.
If you want, Johnson and Weld are old style liberal Republicans, pushing the "socially liberal, but fiscally conservative" line that was popular in the Eighties and Nineties. Don't say that it's impossible to be SLBFC, because it's also been hard for politicians to be socially conservative and fiscally conservative.