Aside from Napoleon, despite being called empires, why did most colonial powers never seem to take on the title associated with their territory? George VI is called the King-Emperor of India and I've seen many pre-WWII texts referring to British monarchs as the Emperors of India specifically. However, despite on most documents and titles being referred to as the "British Empire", monarchs are always referred to as King or Queen. To my knowledge until Napoleon this was the case with most of the European colonial powers but why was this?
To my knowledge, there's a very short list of states we say had 'emperor' in Europe. However, there were political positions which were suspiciously imperial where we don't use the term emperor. The ones that come readily to mind are tsar and sultan. Some people call the German Emperor just that, and some people use Kaiser. And of course there is Fuhrer.
The word "emperor" is "imperator", Latin, which (IIRC) was a Roman rank prior to Augustus, who coopted the title among his others. The HRE (in case you couldn't tell from the name) was a conscious claimant to Roman political legacy. The Eastern Roman / Byzantine Emperors did not use the term imperator, nor any relative of it, but basileus instead. That said, they also were claimants to Roman political legacy.
Kaiser and tsar are both derivatives of Caesar; claimants to Roman legacy, too. Seeing a pattern?
Napoleon directly took the title emperor, but also retained First Consul of the French Republic. The Consulate was a period of French governance between the Directory and the Empire, but the choice of name should be telling. I posted a link further down in the post which will tell you more.
Use of the title Emperor of India arises from the Mughal Empire. The Mughals (IIRC, it's hard to find a good non-wikipedia source for this for some reason) included no relation to the Roman imperator, but instead, Shahanshah (king of kings, title of the Persian emperor), sultan, and khagan (Mongol autarch).
To be sure, I have no idea where the practice of calling Persian Shahanshah / Padishah as 'emperor' originates. The term seriously post-dates them, and has very different connotations. Additionally, Mongol emperors aren't generally called that, most often the term Khan is used, despite being incorrect (khagan is more accurate). Chinese tianzi are called emperors too, and there is the Emperor of Japan.
As you can see, titles have strongly historical connotations. The use of Roman terms in Europe inevitably has cultural associations with the Romans and just how awesome everyone thought their empire was. That's the cliffnotes - the religio-cultural implications are immense. This book has good discussions of several cases, and I've linked you directly to Napoleon's part.
So why didn't European rulers adopt the title of emperor? None of them wanted to play around with Roman legacy. This is a case where why something didn't happen is probably confined entirely to speculation, but you can see a number of valid reasons why a politician wouldn't want to parade around as the Roman Emperor of England, for example.
However, I have absolutely no idea why we call the padishah an emperor. My hunch is it lies in post-Roman historiography, but perhaps someone else knows. Many foreign 'empires' do bear superficial resemblance to the Roman empire, particularly the Persian states. But, for example, the emperor of China was someone who ruled culturally related groups and the term used, China, refers to the region and not the state of origin (like Rome or Persia).