The difference is that, regardless what members of this community thought of it, the Vision Cone wasn't well-designed for new players whatsoever.
First, the control of the cone was cumbersome. The pass progression reading was still the responsibility of the player, with or without the cone. Once the player identified an open receiver, he had to move the cone to the receiver (either with the right stick or R2+button), _then_ throw the ball. I argue that this is too many control inputs to simply throw a pass with a reasonable chance of success.
The vision cone also wasn't well designed with respect to teaching players how to use it and where to point the vision cone to succeed with it. There was no success or fail indicator to indicate that the player was going through his pass progressions properly, that he was doing a poor job using the cone, or any indicators as to how to improve his skill using it. The only feedback was success or fail of the pass after it had been thrown, be it with an inaccurate pass to the intended receiver outside of the vision cone or an interception. This wasn't nearly enough, and resulted in a lot of user frustration.
Between the slow ability to control the cone and no in-game teaching of how to effectively use it, it was almost impossible for a new player to learn how to use the vision cone effectively while playing the game.
In contrast, the tackling cone requires no additional input whatsoever. It's a context-sensitive helper for players to put themselves in the best position to make a tackle. It's completely passive and doesn't itself change how the user plays the game; it merely provides a visual aid as to how to time the tackle control input for various tackle types.
By providing obvious useful contextual feedback to the player without interrupting the normal flow of the game, the tackling cone is much better design and does a better job teach new players how to play defense in Madden in one of the most fundamental aspects of the game, tackling.