Perhaps phrase the question differently, to challenge the premise it is 'cheaper': "Could they set up a datacentre as an independent subsidiary that they were

Perhaps phrase the question differently, to challenge the premise it is 'cheaper': "Could they set up a datacentre as an independent subsidiary that they were client to, but that was run on a commercial basis for other customers too?" i.e. commercially viable. If the answer is "Yes" as it was for Amazon years ago, then it seems like a no-brainer - do it yourself. Otherwise, such decisions calls for greater scrutiny. For example, should HR services be run internally, or outsourced. Outsourcing some functions don't work even they're more expensive on first analysis, like the network effects internal HR can have, or the answer may be "No" for some services, Payroll a common example.