There might not be a reason.

History has happened once, we are dealing with a sample size of one. Given that, any of the following three mutually-exclusive statements about our sample could be true:

• It was certain the Industrial Revolution would occur in Britain before anywhere else, due to a crucial advantage or set of circumstances unique to it.
• It was probable that the Industiral Revolution would occur in Britain first, due to the relative circumstances of it and other countries.
• It was unlikely that Britain would be the first country to experience an industrial revolution. We've rolled a 6 on a dice, and now we're trying to explain why we were always bound to have rolled a 6, when actually it was only a 0.167 chance that that's the outcome we'd get.

That qualification is crucial when dealing with this question, whatever explanations we might come up with. Perhaps it was the unlikely outcome that went against prevailing circumstances. That position is presented much better than I am able to in this classic article by N.F.R. Crafts.

That article is also offers many other answers to your question, being a survey of the literature up until 1977 that address precisely this issue. This covers many of the economic and innovation-based explanations, as well as some of the demographic ones, that are still in circulation.

Of course, history has also developed since 1977, though that article is an excellent starting point. It would be impossible in a reddit comment to even begin to cover the multitude of relevent approachs that have developed. Instead of doing that, I'll highlight just two that have been particularly important.

One is the work of E.A. Wrigley, who comes from a demography background. His most recent work focused on access to energy, as determined both by natural distribution of resources and geography, and by the intensity with which energy resources could be and were worked.

The second is the work of Joel Mokyr, who has braved charges of Whiggism to try and reentangle the threads of intellectual and economic history. His argument is not that Science paved the way for Industrialisation, but that industry and science were manifestations of the same philosophical activity. His argument seeks to encompass both traditional technological accounts and more modern orginisational or social accounts of the nature of the change in production in the C18th.

Refs:
E. Wrigley (2010) Energy and the English Industrial Revolution.
J. Mokyr (2012) The Enlightened Economy.