I haven't seen when a red card offense like foul will lead a more than one match suspension when you didn't insult the referee or players on the field. It's a fair judgment depsite the gravity of what Mbappe did. However, Mbappe should be careful with the way he is macking his opponents and should not do it out of anger or frustration to avoid this from happening again next time.
That means you've not been following the La Liga if you say this. They can suspend players if their intent was not to get the ball but to foul a player. Mbappe didn't go for the ball, he went straight for the legs of the player, and he did not simply trip him and go with a sliding tackle, he went with a kick and a very strong one at that.
Tackles like that are usually reviewed by a committee of RFEF. They can decide if such a challenge should have more game suspension or not. It's not only when you insult an official or fight a player that you can be suspended.