Coca-Cola from a pub or restaurant.

[Usel]

Why is Coca-Cola from a pub or restaurant (not fast food) pretty much always flat yet lemonade from the same mixer tap is always perfect.

Will usually buy it in the bottles or cans if available but when complaining and sending the drinks back upon visiting the same establishments again at a later date it's still flat.

Is mixing Coca-Cola syrup with carbonated water more difficult or something?

 

[Usel]

I don't know about Pepsi as my missus won't drink Pepsi.

 

[Usel]

Coca-cola is her go to drink when driving and she usually drives so this is becoming a wide spread problem for her.
McDonald's does it perfect all the time, I just find it strange how some of the best pubs in England know how to prepare and handle beer but Coca-Cola is a complete fail.