Nobody wanted this but since it is for the urgency for the country to protect others then, such measures are needed to stop the spread somehow.
Both the article and the video mention daily exercise as essential.
And related to that: Have experts in countries with dont-go-out-even-for-a-walk really come out and said that's "it's important that everyone stays indoors in the entire country"? I mean for such a measure you'd expect some good evidence that it works...
People also use "walking outside" as an excuse to gather and congregate - or they choose crowded places for their walks, which is just as problematic. It's just easier to forbid it altogether, and then use discretion to forgo punishment for those who are actually taking sensible precautions.
If the stroll outside isn't the problem then don't ban it. Don't ban outside walks because people walk outside to a 50 person gathering. Ban the gathering.
As you say, they probably don't fine people who go outside and don't go near anyone. But the thing with bans you don't enforce equally is that people tend to ignore them eventually.
And you also only have a fixed "budget" of restrictions. You don't want to waste any of it on measures that don't have an effect. House arrest for a population for 3 weeks is a large chunk of that "budget".
There’s probably a good reason for limiting people being outside - maybe to limit congestion on public transport which isn’t technically a gathering but was a major problem over the past few days?
Which is still allowed:
> That is why people will only be allowed to leave their home for the following very limited purposes: [...] one form of exercise a day - for example a run, walk, or cycle - alone or with members of your household