I wrote a response to this specific question a while back. I'll copy paste for laziness:
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 -- first by the German Ernst Haeckel in September 1914 and again by Charles à Court Repington in 1920. There is no international organization or cabal of historians 'naming' things -- it's just we call it what people call it and things stick. Most importantly: World War One was not called World War One at the time. It was called the Great War for a reason; the people at the time recognized its superior level of involvement and scale but did not call it a world war at the time. That title only came after WW2 and people looked back and said, man, that 'Great War' really wasn't all that different from this albeit just a slightly smaller scale.
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. They weren't 'global' conflicts in that respect they were localized conflicts with localized goals which just had extended fighting -- every single war you listed fits that bill. Outside of the Mughal Empire in the 7 Years' War they're all European powers. The First World War was the first truly global war which hit every single continent. Japan and China and East Pacific colonies, India, Australia, South, East, North, and West Africa, Eastern Europe, Western Europe, the North Sea, Brazil, Central America, North America. Every single corner of the Earth, all from independent or quasi-independent dominions (Australia, Canada, South Africa, New Zealand) operated as independent military entities and as independent government actors. That had never been done before, ever.
You wouldn't call the Gulf War a 'world war' even though it was the U.S. & Friends (America & Europe) vs Iraq (Asia), would you? It had global participants, significant casualties, etc. It's the same thing here honestly: A 'world war' is not just who is fighting but scale. No one was unaffected by WW1 or WW2. Yes it was started in Europe but its participants not only went beyond Europe those directly and largely affected were as well. 1.5 million Indians would volunteer to fight, America drafted nearly 3 million people, 40% of the Australian male population would enlist, fighting would occur off the coast of Brazil and just about all of Central and South America would come on the side of the Allies as independent, sovereign states. China would send tens of thousands of men to contribute to trench building and also providing supplies while Japan seized numerous German colonies in the Pacific in blatant expansionism. Africa was a theater of independent, quasi-independent, and European fighting forces that raged throughout the war.
Numerous, global belligerents had numerous goals (America expanding trade power in the post-war world, basically any laundry list of European reasons, Ottomans pushing into the Caucasus' of Central Asia and firming their grip on Egypt in Africa, Germans expanding colonial gains by creating a continuous German state across about all of South Africa, Japan taking control of European pacific holdings and trying to force China into basically a protectorate, Australia/Canada/New Zealand/South Africa all developing national identities and using the war as justification for true independence, dozens of Middle Eastern tribes tearing the Ottoman Empire apart for independence, Slavs fighting for independence and unification from the Austro-Hungarians and the Russians trying to enforce such, etc.
That's really what separates it from every other global conflict before it (though the 7 Years' War and Napoleonic Wars are the only ones which can really be shoehorned into that category) -- it was not the Brits fighting in Southwest Africa they were Boers, Rhodesians, and Zulu's. It was Indians going to fight for Britain, not Brits. You see where I'm going with this?
Only a select few people in the world were totally escaped from the realities of this war whether it was direct fighting or economical. This type of global participation was unprecedented and you will never find a war like it because every contender for 'world war' before it (7 Years' War and Napoleonic Wars in particular) are European powers fighting over European 'things' in European led colonies. Not this time: Belgium, Romania, the United States, Australia, India, South Africa, the Ottomans, Mideastern Tribes vying for independence, Hejaz, Japan, Cuba, Costa Rico, Siam. 65,000,000 combatants would participate in the war and 37,000,000 people would die. It was not a European war between European powers for European goals it was a global war between global powers for global goals with significant global fighting between non-negligible sovereign global peoples -- the African, Middle Eastern, and Asian theaters alone justify this point imo without even touching America or Europe!
TL;DR:
It's not called a 'world war' because that's not what people call it. It's really that simple. They're called the Napoleonic Wars because they're centered around Napoleonic France and that's just what people call them. The World Wars are called the World Wars and have for over 70 years so that's what we call them.
The phrase 'world war' comes with arbitrary societal implications though. These previous wars were European wars between European powers for European goals. WW1 and WW2 especially were global wars with global participants for global goals like never before.
Deaths and how many continents one fights on doesn't mean it's a 'world war' because that's a very colloquial term -- it implies a level of scale. Like I said above: The Korean War had belligerents from 4-5 continents taking place, Roman wars would have belligerents and fighting from Europe to Africa to Asia. I know it's counterintuitive but 'world war' isn't about the 'world' part but an arbitrary level of scale which we, as a society, place on it. It implies popular participation of everyone everywhere; not just fighting everywhere but sovereign peoples from all over the world taking place in the fighting in some willing fashion or being directly affected by it. WWI did that like no other war before it and WW2 beat that even more.
TLDR OF TLDR
Because society decided so; so that's that. Fortunately or unfortunately depending on your view it really is that simple. Everything else is just justifying what is truly arbitrary naming convention.
Where I got all these silly ideas from:
Peter Wilson, The Thirty Years War: Europe's Tragedy
John Lynn, The Wars of Louis XIV, 1667-1714
David Chandler, The Campaigns of Napoleon
Hew Strachan, The First World War: Volume I: To Arms
I have a book on my desk right now titled The World War of 1813 (J.P. Riley, 2000), so there is a movement among contemporary historians to compare the worldwide conflicts of the Revolutionary and Napoleonic Wars with the 20th century world conflicts. But you can also argue that 18th Century conflicts like the 7 Years War were world wars. In the end, it's all a matter of nomenclature and perspective. After all, you could say that the Second World War kicked off with the opening of the 2nd Sino-Japanese War in 1937-- but most European historians would start their narratives of the war with the German invasion of Poland in 1939. And the Napoleonic Wars were, for the most part, punctuated by the relatively short and decisive campaigns orchestrated by Napoleon, which toppled the various alliances arrayed against him. It's not as useful for historians to refer to the period as a single unbroken conflict between two set teams of nations.