Video streaming sites don't usually let people access their content from other countries. This is because the owners of those events, movies or shows sells broadcast rights on a territory-by-territory basis. So, one company has the right to show a particular sporting event in one place and a different company has the rights to broadcast the same event, but to an audience in a different place.
In terms of broadcast contracts, it doesn't matter where the broadcaster is located. What counts is where the viewer is. So, BT Sports may have the rights to show a particular event in the UK, but not in France. Therefore, you can only watch that event through BT sports if you are physically located in the UK. If you are in France, you will be blocked from watching BT Sports over the internet and you should subscribe to a video streaming service in France to see that event.