It isn't perfectly clear even in the detailed description whether any other link was available, but I tend to suspect that if anything faster had been, then it would have been used in preference to the one that actually was.

It's a cable going between entire countries that got cut. Anything inside the country should still be full speed.

There is no link that could be used in preference. Any repo that the factory stations could access would be unusable by Singapore AWS. And any repo that Singapore AWS could access would be unusable by the factory stations. But the two ends of the link don't have to use the same repo.