You're not wrong, but this is actually what they're pursuing; the article just leaves it out.
> The goal is not only to save costs, but above all to gain digital sovereignty.
> [It's true] that open source is not necessarily cheaper, [..] it requires investment. But the money flows into internal infrastructure, into the further development of Nextcloud, LibreOffice, and other similar systems, instead of proprietary ones.
> Schleswig-Holstein pursues an "upstream-only strategy," meaning that developments flow directly back into international projects. The state does not want to maintain its own forks, but rather contribute all improvements directly to the main projects, thereby contributing to development for the benefit of the general public.[1]
On a side note, the real key to the project's success is that it's supported by a coalition of the conservative and green parties. They actually value digital sovereignty and longterm cost savings. Contrast that with Bavaria, where the MS lobbyist managed to get them to sign a longterm Office 365 contract…
[1]https://www-heise-de.translate.goog/hintergrund/Interview-Wi...