This may come down to two factors: the setting material has a fearsome reputation for being extremely dense, and the setting itself is pretty distant from what Western fantasy audiences have come to expect. There’s a small but faithful fan community around the setting, but it’s never been a runaway commercial success. It was not long afterwards that the original Empire of the Petal Throne RPG emerged through TSR, and every so often someone else tries to do a Tekumel RPG. However, once Barker crossed paths with Mike Mornard, one of the early playtesters of Dungeons & Dragons, he became acquainted with the nascent RPG format and recognised in it a way to game in Tekumel which appealed to him greatly and was nicely compatible with some of the other gaming activities he’d applied to it. (Though Greyhawk lent its name to the first D&D supplement, that was mostly a collection of rules and didn’t really include any setting information as we understand it.) It did not originate as one – like Greg Stafford’s Glorantha, it had been developed by its creator for quite some time before being used for gaming purposes, Barker having dreamed it up in his middle school years in the 1940s and been developing it in subsequent decades, though he did have some exposure at the time to the wargaming hobby and had been producing home-made Tekumel miniatures armies. The Tekumel setting, designed by Professor Muhammad Abd-al-Rahman Barker, has the distinction of being the oldest published roleplaying game world.