It keeps amazing me that the referee pool is so tiny. It seems the same 5-6 refereres are always involved, especially in the big games.
There's so much money involved in the game, I see no reason why there shouldn’t be enough cash to finance a bigger and more competitive pool of refs to pick from.
Perhaps it would even be beneficial to mix up the refs from the major leagues during the games. So you'd have linesmen from Germany and Italy, fourth official from France and main ref from Spain. There's probably good arguments against it, but I think it would reduce speculation about bent refs when there's more variation (although I guess football is global in many aspects
).