To add onto what Don said, the reason we call them the First World War and the Second World War is because that's what people at the time called them and it's what they've been called for going on a hundred years now. Obviously they weren't the first war that took place across 2+ continents or to involve two powers on 2+ modern defined continents but that's not the point: That's what people called them, it's what they've been called for decades, that's what they're called.

I mean it's literally just that simple. Because that's what they're called. The First World War wasn't even called it at the time, just 'the Great War' -- it is only after its connection to the Second World War that it got that name by default. That map you posted is disingenuous, it wasn't fighting raging across all those colonies and such. Most fighting was limited to Europe, that's just the maximum extent of the participatory powers. However, again, almost all of the fighting took place in West/Central Europe. The Second World War was the first truly global war with global fighting between independent sovereign peoples and the First World War was also pretty damned global as well. See this post for more info on that regard.

I just don't really know what else to say. I tried to go in depth when this was asked in the past but at this point I just don't feel like it's worth it. There is no secret cabal of historians naming things for some objective reason. It's called that because it is. The Napoleonic Wars are called such because of their connection to Napoleon. The World Wars are called such because of their connection to each other and their unprecedented scale. There were plenty conflicts before and after on numerous continents and numerous powers. We as a society dictate what we call things and we have assigned an arbitrary level of scale to the term 'world war' -- it's literally "because we said so".

Another reason, and perhaps the most common modern justification though, is that those wars were European wars which just extended to their colonies which happened to be overseas. The Napoleonic Wars, 80 Years' War, 30 Years' War, 7 Years' war, and so on were European powers fighting for European goals and fighting other European armies in European colonies. Thus it's Eurocentric to call it a 'world war' -- 'world war' implies both global devastation, fighting, and most importantly world wide independent actors. However, again, this is all horribly arbitrary. It's literally just "because society says so"

Well, the reasoning behind this is the same as why I refuse to accept the Seven Years War as the First World War. Calling either the First World War precludes a certain level of Eurocentricism that would make even me uncomfortable because these two are European conflicts. The blue is not independent nations around the world but colonies of Euorpean powers that were indirectly engaged by order of the Mother nation.

To make it a "world war" it would have to require independent non regional powers (as in not European powers) to be involved. China isn't involved and Japan is still in isolation. The Ottomans were not very involved, India, parts of Africa, South America, and parts of North America are only involved because those lands were directly claimed by European powers and not independent.

The lack of non European powers involved prevents this from being a world war.