Consider this sentence:
- Since winter, I've increased my training.
Did winter make me start training? Maybe? Maybe not? Maybe the two are related by timing, but one didn't cause the other.
- Since the competition was announced, I've increased my training.
This feels different. Reading this version, we assume that the announcement caused the increase in training.
The point is that context matters
'Since' establishes a relationship in time, and the content and context tells us whether there is also a cause and effect relationship.