This deals with a few issues in relation to steppe society:

Steppe nomads didn't usually individually own land. Normally, clans moved from a summer to a winter pasture, which was sort of their collective land. Within the clans there were probably disputes between families over who was grazing where, but most disputes would have been over the livestock themselves, not the land.

The other point is that just because Ghenghis Khan conquered half of Eurasia, doesn't mean that he owned half of Eurasia. These regions were divided up for governance in a quadripartite system. And again, just because you ruled a region doesn't mean you owned it.

Land ownership in steppe societies typically revolved around hunting reserves. We see this in the Gok-Turk and Khazar Qaganates, where the ruler had a large swathe of land set aside as a hunting reserve for his personal use. However, it was not just exclusively a hunting reserve, as the primary (mostly Byzantine/Armenian) sources preserve that this area also somehow doubled as an arsenal. Wooded areas obviously were important since wood was rare on the open steppes beyond meager scrub, and you needed proper trees to make bows, arrows, and saddles. So forested hunting grounds were valued both for the meat they provided, their use as a training grounds (hunting = training in steppe society), and for the wood they provided for weapons and equipment. As a result, these areas were divided up among the higher ranking individuals of the steppe state and were considered individual property.

I do want to point out though that considering Basil II typically makes the list of "top 10 richest men in history" with an annual income of an estimated 1000 pounds of Gold, then Attila the Hun would outrank him with an annual income of 2100 pounds of gold.