Your butt does not do that. If you are relatively fit, there often is a butt crack gap on top of the bowl. Butt much worse, there is also a bigger gap between the seat and the bowl. If you go from the back there is more toilet bowl in front of you to error in.
Why not from the front? It makes way more sense. Easier to aim and your butt seals against the back edge of bowl hole so the water doesn't splash out.