Think about the motion you're making on that play, you're concentrating on catching the ball first and foremost. That throw, unlike say, the return bounce when you're dribbling a basketball, can get to you in a wide variety of locations and the runner could be sliding multiple ways which changes your tag target. That means there isn't a muscle memory that when you catch the ball you make this specific movement and that's a clean tag every time.
You're taught(at least I was) to bring the ball to the base, the runner has to get there. At the MLB level it's not exactly that simple, but that's the general mechanic. You can see Swanson doing a version of this, but he came in a little low and the ground slowed the sweeping motion just enough for the runner to be safe. The other end of the spectrum is if you come in too high, a hand can sneak in under you.