Why would you call colocation "building your own data center"? You could call it "colocation" or "renting space in a data center". What are you building? You're racking. Can you say what you mean?
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Cloudflare has also historically used “datacenter” to refer to their rack deployments.
All that said, for the purpose of the blog post, “building your own datacenter” is misleading.
I don't know what point you tried to make. Any business in the whole world survives because they sell things for more money than what it takes to keep their business running. Is it surprising that they charge their customers more than their infrastructure costs?