Prices on Steam are set arbitrarily. Getting things at "50-90% off" could just as well be described as sometimes getting them at normal price and otherwise getting them at 2-10 times normal price.

It's not a used game market unless you can transfer it to other people an unlimited number of times without the original company getting a say.

I have no idea what world you're living in. No prices on Steam are anywhere near 2x the "normal" price, let alone 10x. Companies that set their prices to the typical MSRP are generally seen as largely out of touch (with Japanese companies being particularly renowned for this), let alone above MSRP.