The attached file has two simple curves. In the Left viewport, I am trying to split the horizontal curve with the vertical one. It refuses and reports: “Split failed. Objects may not be within tolerance of one another.”
I guess the difference is in the workflow- with Trim you get instant action- the thing you click on goes away - so you can move from view to view and have the trim take into account the apparent intersection from that exact view when you click. Split does not do anything until all the splitters are selected and then all the splitting is done. It does not keep track of which view each object is picked in.