Nike certainly could choose to sell at a discount rather than grind unsold shoes into rubber. They have a wealth-signal brand to maintain, however, so they will resist doing so if at all possible.
Is it really the case that Nike is a wealth signalling brand? In the investigation I think you're referring to (https://www.fastcompany.com/90697259/nike-appears-to-be-shre...), I find Nike's side of the story much more plausible: if they find in processing returns that a shoe appears to have been altered, they prefer to reuse the shoe materials for other purposes, rather than carefully inspecting individual shoes to analyze what the alterations are and whether they might compromise the shoe's performance.
Nike is famously one of the less wealth signalling shoe brands. Until recently I don't think they had a product for sale for more than ~$220 at all.