Probably the main reason many kits call for tea is that a lot of them are based on the SAS survival kit. You must remember a lot of so called experts regergitate much that was written by someone else. Without any personal experiance or research. The SAS book was written by a Brit. So tea being the national drink. What else do you think would be recommended.

But there is one advantage that tea does have. It can be made at much lower temperatures. Coffee, even instant requires boiling or very near boiling water to make. While tea can be steeped at room temperatures. Any of you ever made sun tea. While a hot drink may be good in cold weather you can get your caffine fix without building a fire. All it takes is more time. There might be times you can't or don't want to build a fire but need the caffine.