Because otherwise it really doesn't feel worth it. Not everyone has such high amounts of legendary shards that the costs are irrelevant, and for those that do it's not like these high costs are gonna drain their reserves. All this serves to do is hurt the people without high shard reserves. Edit: Yes, I know about the legendary shard farm glitch, but that's irrelevant because we all know bungie is eventually gonna patch it and then this is gonna go right back to being a problem.