Off a tee the ball is stationary and lifted off the ground. Kicking fieldgoal, the ball is always in motion. From the snap, to the set, to the spin. I remember awhile back, the NFL went to a shorter tee because there were so many touchbacks, so the height of the ball off the ground has something to do with it for sure. Then there's that running start. On a fieldgoal attempt, a kicker gets maybe 3 steps or risks a block.
Feel small yet?