SSDs have no physical tracks or sectors and no mechanical movement. Thus, SSDs can reach logical block addresses (LBA) much more quickly than HDD heads can physically move. Because SSDs have no moving parts, there is no mechanical seek time or latency to overcome.
Even the fastest HDDs cannot keep pace with SSDs in a high-demand I/O environment. Parallel disks, caching, and additional memory certainly help, but the inherent physical disadvantages have limited the ability of HDDs to keep pace with today's seemingly limitless data growth.