Apart from the obvious answer of Britain being an island, so the best defense against invasion would be to stop them in the water, and the exception of land-locked countries like Austria. How come other European powers fell behind in terms of their navy?
Why is the obvious answer insufficient?
How much military can a nation afford? All of the Continental European powers had to invest quite a lot of money in their armies. They needed to do this because they were vulnerable to land invasion by other European powers.
If a country needed to invest a lot in an army, it had less money available to invest in a navy.
Britain, thanks to being an island nation, always had a small army. This left Britain with more money than other European nations to invest in the navy.
It's not like they didn't try. France was a challenger in the navy game, especially in the Napoleonic wars.
And the German empire actually put the fear in Britain in the late 19th and early 20th century with its rapid navel expansion along with arguably the strongest army in the world. They could really dominate he colonial game and that was a cause of the major friction between the empires in pre-WWI.
What really set apart the Royal Navy to other fleets was experienced officers
Culture of the Royal Navy placing an emphasis upon the positive examples of Nelson and the negative example of Byng. This resulted in a bred of sailor that knew that courage, aggression and determined assault were the highest qualities in a fighting man, that failure to show these characteristics would be severely punished, and that 'no man who placed his ship alongside the enemy could do much wrong.'
Geographical location and the seizure of Malta, Gibraltar allowed Britain to easily block other European nations access to the sea. Royal navy got first call on funding, whereas land powers could not economise on their army. Social acceptability and recruiting base. Not other nation had this combination of factors.