Title says it all. Why is it romance languages only developed in those specific areas? Or did some languages do develop but then died? It would be super interesting to hear what those languages might have sounded like! Apologies if a similar question has already asked, I am on mobile and the search function super sucks. Or if this would have been better placed in a different subreddit
Here are some earlier answers about Britain and Western Europe:
u/Stormtemplar answers Questions about the history of the English language!
u/EnricoDandolo answers Question about the spread of Latin in the Western Roman Empire
u/bitparity on Why did Britannia fail to Latinise?
On the subject of Romanian, several old answers are listed here
I think you have to be a bit more specific than that to get a good answer, Britain has a vastly different history than the Balkans, and they all differ from the Romance languages, so you have to examine each specific case to really get in-depth.