Since reading your comment I’ve noted that I don’t use since and because interchangably. I believe because puts emphasis on the reason, while the main focus when using since still lays on the thing being explained.

“I take the left here, since that route is shorter.” – (Slight) stress on the first part, the latter is “just” a justification.

– “Why do you take the right when the left route is shorter?” – “I don’t take the left because it is shorter.” Stress on the last part, it’s the main point of that sentence.