The intent is to provide players with a sense of pride and accomplishment for unlocking different heroes. As for cost, we selected initial values based upon data from the Open Beta and other adjustments made to milestone rewards before launch. Among other things, we're looking at average per-player credit earn rates on a daily basis, and we'll be making constant adjustments to ensure that players have challenges that are compelling, rewarding, and of course attainable via gameplay.
Basically, what they're saying is that they calculated the average credit earn rates to determine the maximum cost that would still be attainable (100 hours of gameplay). And then lootboxes, of course. Classic Orwellian duckspeak. Quack.