Well, the very simple answer is that it's not a global standard. Here's a quick google search to illustrate my point. Pacific-centric maps a very much a thing that exists, and are used more often in countries like Japan, China, or Australia where the Pacific is much more relevant. I even personally prefer them. So the question becomes more, why is the Atlatic-centric map more common in general, or at least more common in your life.

The probably answer is that where you live, Euro-American politics are more relevant and/or your country is on the Atlantic. I know that the North American countries are on both oceans' coasts, but they are uniformly more connected to Europe culturally and politically than they are to east Asia and the Pacific. So that's reason number one.

Reason number two, and the reason why Atlantic-centric maps are more common in interantional contexts or countries that aren't focuse on either the Atlantic or Pacific is European (and American) cultural and political dominance in the last 400 years, which are coincidentally also the 400 years in which there has been a focus on detailed and accurate cartography. China and India have massive populations, but until the last 70 years they weren't power players in global politics. Meanwhile, Europe colonized, conquered, or traded with everyone. European political models were widely adopted (or placed) in many non-European countries, and Euro-American culture are omni-present in most of the world.

Despite their relatively low populations, European and American countries dominate world politics and economics and have pretty much continuously for centuries. As a result, their map making preferences have proliferated. Though, as I said, they're certainly not the only option in use today.