Here’s the thing to understand: The things libertarians want - freedom, less govt. interference in markets & in personal choices, non-interventionist foreign policy… there is no money in these things for politicians. There are no big corporations and very few rich people who are willing to pay tons of money to politicians to refrain from intervening in markets, or to keep the troops home, or to let people ingest whatever substances they want to.
In fact, it is just the opposite: Corporations have long been in the business of paying politicians to intervene in markets on their behalf, to erect barriers to competition and in some cases to squash a particular competitor. Competition is wonderful for society as a whole. But it’s not so great if you’re one of the ones doing the competing. It’s hard, and sometimes you lose. Sometimes, if you’re big enough, it’s just easier to send some money in the direction of the people who can discover antitrust violations in your competitor’s business practices.
Understand that behind the empty campaign promises, politicians have essentially two things to offer to the people who support them: 1. Power, in the form of regulatory and other control, over competitors and others who may get in the way of a particular entity remaining comfortably profitable; 2. Money. Not their own money of course - your money, and my money. Taken from us in taxes, and in the continual devaluation of the government-issued money we all use. Politicians can give money to their supporters in the form of contracts for things like military equipment and public works projects, or in less direct ways, like mandating that government schools all stock epinephrine injectors that meet the same very specific product requirements that your device happens to meet.
And the list goes on. What is not on this list is liberty. Why? Because nowhere in this game is there an advantage to selling liberty.
This is the real reason that libertarians “don’t matter” in the political sphere. It’s not because they don’t vote. It’s because they don’t participate in the real game of politics - the interest-driven game that can never reward a player who wishes to dismantle the very engine of that game. People win at the game of politics by buying and selling political power over other people’s lives and resources. A player who wants to reduce that power will not find themselves rewarded within that game - they will find themselves spat out of it.