It's not that simple. There already aren't enough hospitals for everyone that's getting sick, and they could build more, but that takes time. They would have to get equipment and doctors for the new hospitals, if equipment isn't available, more has to be manufactured, if doctors aren't available, more people need to go through medical education. All of that takes time, and the only way to buy more time is by slowing the spread.
If no one took any measures to slow the spread, each infected person would infect one more person every other day on average.
That might not sound like much, but it effectively means that every other day, the number of infected would double. After just 2 months, every person on the planet would be infected. How long do you think building hospitals, manufacturing equipment and training doctors takes? The governments can't make magic happen. That's why people need to take this seriously.