I noticed this trend around colleges, but also in some small businesses, of people being given official email addresses but preferring to use their own. Reading the article, that sounds like the case here. The government employees are preferring to conduct business with email addresses they've had for years rather than their official address, perhaps even forwarding their official address email to their personal email address.
On the other hand, at least here in GA I've noticed that many small businesses have stopped self-hosting email, if they ever did to begin with, because it was cheaper to contract it out. They could get greater reliability for a reduced cost compared to having (potentially) additional IT staff to handle the workload associated with it (same with other hosting services). Or if they were too cheap to hire the additional staff, as one company I saw was, the IT staff convinced them to outsource it so they could free up their time to work on things the company actually needed them to focus on.
On the other hand, at least here in GA I've noticed that many small businesses have stopped self-hosting email, if they ever did to begin with, because it was cheaper to contract it out. They could get greater reliability for a reduced cost compared to having (potentially) additional IT staff to handle the workload associated with it (same with other hosting services). Or if they were too cheap to hire the additional staff, as one company I saw was, the IT staff convinced them to outsource it so they could free up their time to work on things the company actually needed them to focus on.