Wow, this is really fascinating.
To answer the OPs question in my own words, it’s that the eastern Pacific as well as the North Atlantic have divergent plate boundaries while the western Pacific’s boundaries are convergent, which is probably why that region has so many islands and volcanoes and certainly has an interesting visible effect on the sub oceanic geography.
Not sure what’s confusing about the southeast pacific, looks like there’s one range over the nazca and Antarctic plates and one over the pacific plate with a valley in between.
