The biggest down fall was the clip and mag. If you had been in any kind of exchange of fire, how much ammo do you have left? So now you are going to jump up and rush a position with a rifle that you don't have a clue how much ammo is in it? And it isn't the easiest to pull out the ammo that's in the rifle and replace it with a full clip especially while somebody is shooting at you.
Reloading a garand is a quick, one handed operation. Pull bolt back w/right hand to eject round in chamber, push clip release w/right thumb (one swift motion) and partially loaded clip pops up into your (right)hand. Insert fully loaded clip and you're good to go in much less time than it takes to read the instructions.
While the M14 has a 20 round magazine as opposed to the Garand's 8 round clip, the fact remains that you do not necessarily know how many rounds you have left in it either. Clip can be replaced as easily as the magazine and in about the same time frame so about only advantage (other than increased mag. capacity) is that you can replace magazine w/a round still in the chamber on the M14.
The Garand may not be the greatest rifle ever
invented, but it was darn close in 1936 when John Garand developed it.