I don't quite understand why they're even mentioning Bitcoin if what they use is, if I understood correctly, just Blockchain but not for currency purposes. There've been minor projects offering something like this, and now one of them is becoming big because of collaboration with Microsoft.
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When we are talking about securing IDs, we need the safest blockchain that exist, and that's Bitcoin.
Creating their own blockchain with own incentives and enough miners would be either clumsy, expensive, unreliable or centralized and borderline illegal, and would probably defeat the purpose of why to use blockchain at all.
With Bitcoin, miners are already in place and any upkeep of the security takes care of itself.