Its not as simple as picking another route. When a large submarine cable breaks, what happens is packets are routed through alternate (read longer) routes to reach their destination. The sudden surge in traffic on these other routes also causes a congestion and brings entire networks to a crawl. Even though only the route to the US is currently broken, connectivity to sites/locations that are not within Malaysia will be equally slow due to the congestion brought upon by the additional load using the alternate routes.

Think of it as a road, if all the lanes on the highway is blocked, drivers automatically decide to take the trunk roads etc. But the trunk roads do not have the capacity to handle the traffic that the highway handles, and eventually it gets congested and crawls as well - and this very fast overflows to other roads and congesting them as well.

But the submarine should have special machine to put the cable system under the sea right? The special machine must strong enough to withstand the sea's pressure level to allow the cable system work to be done. Eh expert can explain?