Why don't all sporting activities have the same warm up?

Because not all sports requires the same body movements or parts.

Explanation:

For example, a soccer player will stretch his legs but not his arms unless he's a goal keeper. A baseball pitcher will warm up his arms more than he will his legs because he'll use them more than he'll use his legs

Because different sports require different stretches and warm-ups..

Explanation:

take football and gymnastics for example. for football you don't have to do the splits and practice cart wheels, and for gymnastics you dont have to be running routes making up plays..