It's been a while since I played too - since before carriers were a thing in fact. My assumption would be that the carrier's purpose is to transport vehicles a long way, and for that they'd charge an amount. Whether you're charged on the way in, just before it jumps away, or upon arrival, no idea I'm just riffing really, but I assume that as carriers are not only expensive, but they accrue expenses over time, that the owner needs to make money from it.