In my country we have the private keys directly inside our citizen card since the last 20 years, now is even becoming contactless on the next iteration. We can sign events or PDF documents that digitally prove our identity. Still, the private keys are passive to interception. There is no way to prove that a rogue party is not copying the private keys. About 50% of my country does not vote, it would be easy for the largest party with key employees everywhere inside the gov systems to leak who hasn't been voting and to cast the vote on their behalf. There isn't a need for tax records, we have an accurate registry of who is a citizen and still we wouldn't vote digitally without physical verification because of fraud. That is the reason why we keep using paper ballots and physical voting with parties in the room to check what happens. Identity verification is the key aspect that needs to be assured.