Modern motherboards have increasingly been short on USB headers. For example a rear bracket with 4 USB ports has been available for years.
Today however the bracket has largely given way to USB cards which are actually less expensive.
Most recently USB 3.0 PCIe cards have largely replaced the older USB 2.0 PCI cards. Still there are some recent motherboards with old style PCI slots to support existing hardware.
Today with the proliferation of USB 2.0 hardware such as The HX1000i PSU and the WiFi card the demand for USB exceeds the available ports. Front panel USB ports want in on the headers as well as flash card readers.
Fortunately there are mass produced components to deal with the problem. Low cost USB 2.0 hubs are ideal for cable management. Extension cables are also available to easily place hubs on the motherboard tray.
The top USB hub has the undesirable feature of being vertically mounted while the lower USB hub is 90° angled. The angled design can be placed on the back of the motherboard tray easily with lots of clearance where cable management is dramatically easier.
Double sided tape can conveniently attach the hub to the motherboard tray. USB 2.0 can be 5 hubs deep without problem. If several spitters are needed they should be branched out. Extension cables are widely available.