The switch scenario implies that the individual has responsibility for the entire system. The switch and the train have a strong cultural component that implies responsibility for the system as a whole (employee). Even if you state it explicitly people simply don’t believe that a train switch is going to be left unattended and put into the hands of a completely independent third party. If you state that the train switch operator dies while you are visiting the station leaving the switch in your hands there is an implication that you are stepping into the switch operators role.
Society expects that someone with responsibility for the entire system would make trade-off decisions that would be immoral in the second scenario. For example, a politician would be expected to make policy of when it is acceptable to harvest organs from a donor while a doctor making a decision unilaterally would be morally repugnant.
The questions are more interesting in getting insights into cultural expectations of responsibility than deep biological biases about morality. It turns out that we have very finely tuned expectations on what rises to the level of “responsible” that moves a decision from one category to another. A health minister making a decision about which medical treatments are medically necessary are seen as less morally ambiguous than an insurance executive even if the process to make the decision and the outcomes are exactly the same.