A carrier turns down a cheap rate when the truck payment, the driver, and the miles home do not fit.
You can argue the rate. You cannot argue the truck payment out of existence. Insurance, tires, and an empty mile back to the house are in the number whether the load board looks soft or not.
Ask what the rate has to cover
If a carrier says the rate does not work, ask which piece does not work. Sometimes it is the deadhead. Sometimes the dock time eats the day. Sometimes the truck note is the whole story.
A rate that looks fine on your spreadsheet and will not cover the truck is a rate you will not cover. Find another truck or pay what the trip costs.