Legacy, and corporate requirements. If you're in IT-ops supporting thousands of users running line of business applications across several continents you want all the control you can get. Especially if the l-o-b apps have anything to do with managing customer's funds, investments, well being etc.
Consequences of not doing so could be catastrophic, one rogue trader at a Singapore branch bankrupted a major UK investment bank, imagine what 5000 rogue traders could do to Gold in Sacks
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