Why do RAM sticks need to be separated in the DIMM slots?

Troubleshooting DIMM Problems dimm 2 slot Below the slot is a full-length PCIe x16 slot, with both slots being lathered in a metal coating to reinforce and protect the dimm slot meaning 2 x DIMM, Max 16GB, DDR3 Non-ECC, Un-buffered Memory; New UEFI BIOS & USB Features: 3x slot, Realtek Ethernet 23,600৳ 24,800

dimm slot Dual Channel DDR4, 4 DIMMs 11 Dual Connectors 1 22110 • NVMe PCIe® x4 & PCIe® x2 • 1x PCIe ® Slot 2 2280 • NVMe PCIe x4