First everyone gets upset that people have been allowed to travel into the country, bringing virus strains in with them, with cries of "why didn't we shut our borders?". When we finally do, there are angry outcries that we're doing so. Sadly, there are so many people who don't care or who are willing to flout the rules, there have to be OTT drastic measures to ensure they really don't....
Other countries have been doing this for a while, for instance Iceland has quarantined incomers since March last year. They fill in forms before flying, take tests which they pay for themselves and are placed in a hotel once they arrive. The quarantine is severe....there's no escape. Sneak out and you're in the middle of a remote lava field....you won't get very far. Not a single chance of ducking it or lying, you go directly from the 'plane. And pay for it all yourself.
Yes, it's to deter people from travelling, why not? We're in the middle of a pandemic! Only if it's absolutely seriously necessary should anyone be travelling, drastic measures will ensure this is so....