IIRC the main issue is that in order to play the reload animation properly, you need to have the gun drop, you cannot work the bolt with the sights up. The reason is because if they did have reloading whilst in sights, you would not be able to stop the animation and run or such, destroying fluidity ingame. The devteam has been over this before, and the conclusion is the same, the fluidity is more necessary than reloading whilst aiming.
That said, they could probably up the reload speed on the SMLE a bit more, even out of iron sights, but it currently is faster than all the other actions ingame. This is especially evident if you hip fire. Either way though, when taking aimed shots at moving targets, no rifle, not even the M1 Garand, provides much advantages in reload speed for each individual shot. It will be generally slow simply due to having to sight back in after each shot, generally on a target that has continued to maneuver, changing range, speed, and cover.