Simplify simplifies based on branch comparison. There is no branches to compare in your case, there is just one branch.
http://www.grasshopper3d.com/m/discussion?id=2985220%3ATopic%3A316698
http://www.grasshopper3d.com/m/discussion?id=2985220%3ATopic%3A1131453
“As you correctly noticed the Simplify action will only work on trees with multiple Branches. When a path is {0;0;0;0;0} it might seem obvious to you that you just want {0} but what if it was {0;0;1;0;1} should it be {0}, {1} or {1;1} or even {0;0;0}?”