Each "bit" in SRAM is bigger than each "bit" in DRAM. Typical SRAM uses six transistors for each "bit", while typical DRAM uses one transistor and one capacitor

Each "bit" in SRAM is bigger than each "bit" in DRAM. Typical SRAM uses six transistors for each "bit", while typical DRAM uses one transistor and one capacitor. Bigger chips means less chips per wafer, and a larger chance for a chip to have a manufacturing defect.