Lets look at the other major players in the age of Colonialism.
Almost all of them had a reset during the Napoleonic wars where they lost most of their territories or sold them . Britain with its Navy managed to stay out of the fray and come out on top
Political stability also helps . Britain didn't have a civil war past 1650 and its transition to a constitutional monarchy in 1689 was peaceful . Rather than the rapid swings between liberalism and reactionaries Britain kept a steady and slow trend of liberalism and avoided years such as 1848 .
France- already infamous
Spain- The war of the Spanish Succession along with the Trieno Liberal from 1820 to 1823 when Spain gave up on many of its colonies.
Other countries like Italy/Germany weren't unified.
Arguably the other great dominator of the Age of Colonialism is actually Russia, It kept all its colonies it gained in the 18th century all the way up to 1991. However Russia was all land based and almost the opposite of Britain in everyway which is interesting.
Saying Russia was a colonist power is like saying the US was a colonist power with Manifest Destiny. Both are technically true but not in the same way as British/French/Spanish/Dutch colonies
Russia and the US were trying to expand their nation states and turn their natives into "Russians/Americans". Hence the expansion being mostly land based.
No one considered Kenya to be an extension of Great Britain. It was a colony of Great Britain.
