Of course, reducing the frequency of contact with other people in general is good. I don’t think anyone is arguing against that. What I’m saying is that quarantine can cause more novel contacts.
Statistically speaking there is a good chance no-one at your work place has the virus yet. We are still counting infections in the hundreds or the thousands in populations of millions. If all you do is to spend time at home and at work, there are good odds you’re just switching between two disease free spheres. You can’t get sick without meeting sick people. The only thing that will change that steady state is contact with new people (by yourself or your coworkers/family).
The point the government was making in this case, I believe, is that quarantine can in fact cause more novel connections, faster, and perversely increase the velocity of the spread. The people who are at home will not just sit there. They will meet other people and those people may be from outside of their ordinary, currently disease free social sphere. Thus new vectors of infection spread are introduced that would not have existed without the quarantine.
A quarantine can certainly help down the road, it’s a numbers game. But right now they’re doing the math and think it would be a net negative.