They still can. A government doesn't have the need for first mover advantage because they have the power to make the official version. Also, the technology is very mature and best practices are better known. The userbase has been trained. And it's cheaper for them to do it now.

Though an official united states citizen email address has its own pitfalls for abuse, scams, and fraud.

Nothing about their organization prepares them for doing this. Having 50000 branch offices and half a million employees is their superpower.