It's telling to look at a comparison of these drives in ark.intel.com. The difference seem relatively minor, with the 5810X mainly seeming to juice active power:
Intel® product specifications, features and compatibility quick reference guide and code name decoder. Compare products including processors, desktop boards, server products and networking products.
ark.intel.com
No idea why, but maybe it was a special request by some customers who wanted more features or found they were throttling in some cases?