Because it's important that recorded information about my interactions with my government doesn't cross borders and escape from the data protection laws in the UK and the EU.
If it was a traditional software system that actually ran on the servers owned by the government then that would be fine.
With GA, at the very least Google get to know when I visit the site, and likely which pages I visit, simply through the requests my browser makes.
I'm not familiar enough with GA to be able to judge how much else is transmitted to them.
I honestly have no idea, and the page on cookies does seem to say that they don't allow google to use the data or do much with it, but that just raises further questions as to how they could ever enforce that.
I guess I'm just very suspicious when personal data crosses borders.
EDIT - also wondering what you mean by a separate deal? If the data goes to the US it goes to the US and is then subject to US laws (and no longer subject to EU/UK protections, deal or no.
If it was a traditional software system that actually ran on the servers owned by the government then that would be fine.
With GA, at the very least Google get to know when I visit the site, and likely which pages I visit, simply through the requests my browser makes.
I'm not familiar enough with GA to be able to judge how much else is transmitted to them.