But updates are promised, so GP's question is valid: where are they, and since they're not there, why? Is this the final product's source code and it has not been modified since?

Parliament elections in Estonia happen once every 4 years so don't expect frequent updates. Next one should be in 2027 so there are still ~5 months for them to publish next update. There was also a municipal election in 2025 and European parliament in 2024 which matches last 3 updates in git history. No elections in 2026 so no updates this year.

If I understood correctly they make updates elsewhere, then update this repository only when elections happen, thus making the repository in the exact state it was used for that election.