Freewill theists take the position that God can't make anyone love him or believe in him. They fault Calvinism because they think Reformed soteriology is coercive.
Yet except for universalists (who may or may not be libertarians), freewill theists believe in eschatological judgment. Some freewill theists espouse annihilationism while others espouse everlasting punishment. But in either case, disbelief has punitive consequences.
And, of course, the Bible often uses the threat of eschatological punishment as incentive for sinners to repent and believe. But from a libertarian perspective, that's coercive. The sinner is repenting or believing at gunpoint. Worse than gunpoint.
To submit because you fear the consequences isn't voluntary consent. Technically, you had a choice, but given the dire consequences of one option, you were acting under duress. Left to your own devices, you wouldn't make that choice. If you're punished for making the wrong choice, then it's not a choice for God, but a choice against the painful alternative.