Have been there? Twice.
No reason for him to be there. Makes for a feel good photo OP to take peoples minds off the royals other problems.
HRH Prince Henry of Wales, third in line of succession for the Throne (of 15 nations in the Realm) is there for more than a photo op. He’s already served as a front-line combat soldier.
The Crown is the symbol of every nation in the Realm — it’s a more important symbol for us, than our respective national flags. The Royal family has a long history of leading by example, in times of strife. Prince Henry is doing his duty, as he sees it. His presence there is worth many times the cost of some extra security. (And, if he draws out some Taliban for killing, all the better.)