Apart from clamping not being fully and clearly justified in most of the earliest specs and papers (which led to a few broken and/or insecure implementations), it makes the whole narrative of the curve being "safe" quite arguable and leaving a flavor of marketing in the mouth (NIST P curves have cofactor 1 so they are "safer" in that respect).
NIST P curves don't require any special preparation to their private key.
Curve25519 on the other hand requires a bizarre "clamping" (https://neilmadden.blog/2020/05/28/whats-the-curve25519-clam...), partially because the curve has cofactor 8.
Apart from clamping not being fully and clearly justified in most of the earliest specs and papers (which led to a few broken and/or insecure implementations), it makes the whole narrative of the curve being "safe" quite arguable and leaving a flavor of marketing in the mouth (NIST P curves have cofactor 1 so they are "safer" in that respect).