This is because the sixteenth note in Bach's polyphonic works should be Legato and the eighth note should be staccato.

Legato with left hand and staccato with right hand are the characteristics of Bach's polyphony, in which Legato is a sixteenth note and staccato is an eighth note. This design is to accurately express the rhythm and emotion of music.

Generally speaking, in relatively fast music, it is more appropriate to play with non-Legato and staccato methods.