all the keys are gone

here you can do it
https://store.steampowered.com/account/licenses/

Some have but it's not a certainty. There have been numerous games since that stipulation was put in place that were offered free elsewhere but then have not subsequently made it towards a giveaway on Steam.

Yes, but that only applies if a directly equivalent offer can be made. Since Steam doesn't allow copy restrictions, and this was limited to 47,000 copies, SQEnix is not, in fact, obligated to extend the promotion to Steam (as it would effectively become a different kind of promotion). Same goes for if there's any sort of check-in or purchase requirement, or similar. Such considerations seem to be a major part of the reason why only a small number of free promos have actually been matched on Steam.

Moreover, there was the impression that Valve introduced that rule to get an edge over bundles and competing storefronts, rather than due to being concerned about freebies [as the first two can be considered to take purchases away from the Steam storefront, whereas matching freebies would actually introduce a similar detriment], so it's unlikely they'd push the matter. Of course, bundles also can't really be matched on Steam..

Even with competing storefronts, the one place where the matter should be clear-cut, storefronts usually add coupons or subscriber discounts or similar to get prices lower than on Steam's storefront. As that discount is out of the developer's hands, they don't have any obligation to match anything other than their base discount price (as Steam, if it really wants to, can also negotiate to offer a comparable storefront discount, if they truly do want to match the offer; Meanwhile, the developer is only obligated to match the part of the discount they're actually responsible for).

Finally, for the few storefront promotions that are more clearcut in falling under the rule- such as Chrono.gg's daily offers- there's actually no clear conception of what kind of timeframe the developer is obligated to stick to, in matching discounts. Meaning, yes, eventually they're obligated to match the Chrono.gg discount on the Steam storefront but, on the other hand, they also have no real urgency to do so.

So, basically, right now, the rule is there, but doesn't seem to have any clear reliability. So far, in practice, it seems to be more of a "some developers choose to offer comparable promotions, but nothing actually happens if a developer decides not to".