It's simply because your partition table is "full".
Judging by the fact that there is no EFI System Partition on the disk, your Windows installation is a BIOS one, which means the disk is an MBR disk instead of a GPT disk. And you already got four (which is the maximum) primary partitions on it, so you cannot create another one even when there is unallocated space.
You'll need to by some means convert
University Data and
Software to logical partitions (which will be contained by an extended partition), then you can create ONE partition with the unallocated space; or you can convert the disk to a GPT disk, which requires you to convert your Windows installation to a UEFI one (and your motherboard needs to have UEFI instead of BIOS for booting that).