Owning DigiD would permit them visibility into the usage of such services. So if the visibility is already there, the victory feels a bit hollow or half-way there.
I'm not even against American big tech or anything but I do feel, perhaps unwittingly, netherlands expose civilians to a lot of negative potential by (mindlessly) implementing their technologies, often simply as a cost decision more than anyhting. There are so many loud voices against it ever since the internet arrived here, but its extremely hard to get anything done on a political/policy level.