Not OP, but my guess is a combination of these two things: Stainless Steel is not only significantly cheaper than Tungsten, but it is significantly easier to machine. Tungsten is a very dense, hard material and likely requires special hardware on the CNC machine that is making these spinners.

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Also, Spinetic is a well known name in the community and in my experience has exceptional customer service.

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Edit 2: Here is a link to tungsten rod. This company ( https://midwesttungsten.com/pure-tungsten-rod/ ) only offers rods up to 1.25 inches in diameter. These spinners are 1.76" (44.88mm), and for a 36" rod of 1.25" diameter tungsten, it'll run you a cool $2149.00. You can buy 36" of stainless steel 1.75" diameter rod for $150 on amazon ( https://www.amazon.com/Diameter-Stainless-Steel-Length-Extruded/dp/B074KHN58N/ref=sr_1_1?keywords=1.75+inch&qid=1578000683&s=industrial&sr=1-1 ) .

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Hopefully that helps.