All sounds a bit fishy to me!
Only last week, Monarch were quoted as saying the route had been a success, with heavy hints that it would be continued beyond the initial trial:
(Western Morning News, 14/2/06)
Leah Rosewell, of Monarch, said: "The route has met all of our targets and expectations and has been a success. We are now reviewing the route to see if should be a part of our summer schedule. No decision has been made as yet, but we are expecting one to be made within the next few weeks."
Sounds to me like they're using the £5 fee as a handy excuse for a commercial decision driven by aircraft deployment or whatever, much as Ryanair used the fee as a handy excuse for dropping one daily frequency NQYSTN during the Winter where their load factors have been pretty average at best.