One big reason is that a fair number of these claims are not associated with Splinterlands or even Hive accounts. It's been almost a year since the air drop ended, but as a refresher it was for assets held across multiple platforms. People had DEC on Steem, had bought cards on WAX, etc. You had to link your external wallet to a Splinterlands account and sign a transaction on that network to claim your air drop. I don't think it's reasonable to put it on Splinterlands to try to track down people who haven't claimed rewards in almost two years, and it doesn't make sense to keep maintaining these records in perpetuity.