Why are Vedas regarded as Apaurusheya (authorless/ not created by anyone)?
Is it a sin to consider that Veda was written by someone as propagated by Western scholars?
As per Brihadaranyaka Upanishad, not just Vedas but all our scriptures are the breath of the supreme being.
Yajnavalkya Maharaja tells Maitreyi Devi,
As from a fire kindled with wet fuel various kinds of smoke issue forth, even so, my dear, the Rig—Veda, the Yajur—Veda, the Sama—Veda, the Atharvangirasa, history (itihasa), ancient transmissions (purana), the arts (vidya), the Upanishads, verses (slokas), aphorisms (sutras), elucidations (anuvyakhyanas) and explanations (vyakhyanas) are like the breath of this infinite Reality. From this Supreme Self are all these, indeed, breathed forth.
The logic is just like a breath of a person is coexistent with a person, the Vedas are coexistent with Ishvara and not created at any point.