Smell is particles. Every product aimed at a bad one adds a stronger one on top. Subtraction is a different mechanism, and it has analogues: glasses that remove part of a scene rather than tinting it, gum that absorbs rather than flavours. The nearest serious attempt was a wearable air product that did not find its market.
The open question. Can an unwanted signal be subtracted locally rather than masked?
What would kill it
Removing a signal locally, selectively, continuously and unobtrusively is a far higher bar than masking it, and the last company to try had the money, the acoustics team and the supply chain.