It’s partially the result of the 2007 cyberattacks they endured. After that, they started taking cybersecurity very seriously.
[0] https://www.tandfonline.com/doi/abs/10.1080/09523987.2020.17...
Quite apart from that, if they really took cyberattacks seriously theyd be voting with pen and paper.
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.