You’ve yet to articulate how voting for a unknown candidate is going change anything or be helpful in any sort of way, because you can’t, and if you were to attempt to do so you’d just be talking out of your ass.
Vote totals are recorded, and the parties look at them after an election. If a party loses by a slim margin, they're going to look at the votes that went to "third party" candidates and think - "gee, we could have won if they'd voted for us. How can we convince libertarians to vote for us? The 'lesser-of-two-evils' pitch doesn't seem to be working."
It gives them incentive to pursue policies that libertarians will find appealing. If we just give them our votes regardless, they have no such incentive.