Their development of IT public infrastructure is a bit more complex. The first thing was the political situation in the 90's during the transition. As they wanted to go as far away from communism as possible, they sliced away all the political tradition and old politicians. A lot of young people got a chance in politics and public policy making. They somehow understood that investing in technology is the way to go.
But the real starter was the Progertiger program, which brought computers to public schools. By 1999, almost all the schools were connected to the internet (about 98% of them and you have to understand that Estonia has a lot of countryside and forrests).
I haven't seen the code nor read about it. But I'll have a look at it after this comment. Thanks.
The e-vote thing seems like an issue of reputation now. I don't think any politician would dare to change this. It would be possible only if a huge campaign involving a foreign interference becomes successful among the voters.
[0] https://www.tandfonline.com/doi/abs/10.1080/09523987.2020.17...