One of the main reasons a person may refuse to accept a settlement amount and go to trial instead is when the settlement offer is not high enough to merit acceptance. In some cases, settlement offers do not accurately compensate the victim for their medical bills, and so, causing them to risk going to trial instead.
Another reason a victim may refuse a settlement amount is to hold the at-fault party liable for the accident. In some cases, the other truck driver may have been intoxicated or violated a specific regulation, potentially giving the plaintiff motivation to hold the at-fault party accountable for their carelessness.