"execution time" in this context can only happen for methods that we observed at the top of the stack at the time when we collected the sample. That means that in your case, for example, there's code being executed in the "forName()" method that causes it to be at the top of the stack in about 75% of the samples. This means that it's the method that's doing the actual work here (or that it has a performance issue).
Methods that just delegate a call to the next tier typically will never have any execution time.
There's an alternative view if you click the three arrows at the top right which groups the samples thread-wise and shows them bottom up (instead of this top-down view here). There you'll see that it'll be mostly leaf nodes, in addition to those nodes that do the actual work in the stack.
In short, an execution time of 0 means that the node was never observed to be at the top of a stack.