This has to do with the lacing options which you can find in the bottom right corner of almost all Dynamo nodes.
In your example the Curve.PointAtDistance node has lacing option set to “shortest”. That means that the node only executes for the shortest list of the inputs, which in this case would be your curve. If you however set it to “longest”, the node will execute for the longest list of the inputs and repeat the last item for as long as the longest list is.
(If you set it to “cross product” it will execute for all combinations of two lists)
Edit: and now I see that it’s not a Point.AtParameter node!