It is reasonable to assign parts of the blame to the different parties involved in an accident. This includes the operators, the theme park itself, the attraction manufacturers, and the guests. If the mechanisms operate as expected and the guest has done something that puts themselves in danger, the park is not at fault.
If, however, there is an incident where it is proved those employees responsible for the operation and upkeep of the attraction are at fault, it is on the company themselves to bear the weight of the responsibility. An employee who dispatches a train car early, causing it to bump into another, can't be the one responsible because they did not design the ride or the safety measures. Those measures should do everything mechanically and logically possible to prevent the operator from letting that train leave the station earlier. No employee should have to be fined or jailed; the employer is responsible for their training and their operation in the attraction, so the company is responsible. It is possible the company itself has responsibility measures in place, and I would support the firing of an operator or maintenance worker who was proven to not perform their tasks as expected, but that is internal and rarely means the person is liable.
Theme parks assume the risk of an attraction when they have it built by a manufacturer. The risk in the daily operation of the attraction is the park's responsibility. There has to be strict delineations of responsibility for the attraction: the mechanical parts that make up the ride, the actual construction, and the operation, to name a few. If a rollercoaster's supports collapse, that is not the fault of the park but rather the manufacturer. If the train dispatches early, that is an issue with the safety measures. If a child under the required height gets into the car, that is the operator's (and the park's) responsibility. Each of these areas of failure can be examined and if one of these are found to be the cause of the incident, that party has to bear the weight of the accident.
It seems to me that theme parks are doing all they can to prevent accidents from happening. Safety is on top of every park's mind, and they realize their employees must be thinking of that too. My best suggestion is to keep the idea of safety up in everyone's mind as they clock in, as they rotate among stations, and as they come back from break. The park, who, in one case, promotes Safety as the 1st key in their 5-key structure, needs to remind folks every day as they step into the attraction to do the work.
Disney doesn't allow smart phones or watches to be on the operator when they're in the attraction. I don't personally like that but understand the reason. Those are great distraction tools and could cause someone to be inattentive. This makes me think that all theme park operators need to strongly enforce all the rules they have in place for the safety of the guests.
So theme parks need to keep safety at the top of every employee's mind in whatever way possible.