Why did many water routes develop across southeast Asia instead of land routes?

It me to understand the world and my place in it. for example, (and i know i’m using the terminology ‘historical perspective’ loosely here; some of my examples may be better termed an ‘evolutionary perspective’) knowing that all humans can trace their ancestry back to a common ancestor who lived in southern ethiopia ~200,000 years ago makes me feel connected to everyone on the planet. knowing that some of our ancestors left africa about 70,000 years ago and interbred with more archaic hominin species in europe and elsewhere, me to see the stupidity of white supremacist ‘purity of the race’ themes. seeing how religion was used to enslave people, and how callously lives were thrown away by those in power in the world wars of the past century makes me feel extremely fortunate to be living in the modern era. and, perhaps most importantly is that this knowledge makes me for the sacrifices our ancestors made to get us to this point, and determined to do my part to make the world a better place for the next generation.