My guess is that server farms are currently used at full capacity. So that while a few years ago the thought was to upgrade existing data centers to more effici

My guess is that server farms are currently used at full capacity. So that while a few years ago the thought was to upgrade existing data centers to more efficient servers, now there is more data centers being built while slightly less efficient servers are left running where they are. This is the accounting change to reflect that: depreciate slower to reflect longer in-practice life. Also "data center electrical power / compute" (which reflects both cooling and server power supply cost) has held relatively steady for a while which makes it easier to do that.