New
#21
Most likely because there is data on that partition up to that 50GB line, physically occupying space up to it. The data could be splattered all over before that point, but there is data written up to it. Can't shrink below any active/used data on the drive/partition.
MiniTool will do it with resize/move option, but Windows Disk Management will not.
Best Free Partition Manager for Windows | MiniTool Partition Wizard Free