The soil in modern industrial farming, which is frequently tilled and treated with pesticides, is typically very barren of the microorganisms amd fungal networks that help to sequester carbon for the long term. Even if some is still sequestered despite this, it's much worse at it than most other soil.

Farming cotton the traditional ways also requires buildings, just as a lab would, and heavy farm equipment (the use of wghich can also compact the soil to the further detriment of the microorganisms) that requires gasoline or lithium ion batteries made with cobalt from the congo.

Rural buildings and scattered land use are typically more disruptive to ecosystems than when human activity is concentrated to the smaller footpelrint of cities.

Labs can be put anywhere, whereas cotton farms are limited by space and climate to certain areas, so using labs in a variety of areas might mean much lower transporation costs and gasoline use between the cotton producer and the manfacturer that buys it.

Large scale farming also equals large scale deforestation, replacing complex ecosystems with monocultures that are routinely uprooted. This means both worse carbon sequestration and also worse stuctural cohesiveness of the soil (no roots and fungal networks holding it together), making areas more prone to landslides.

Also farms tend to pollute the groundwater all around them, and they displace native plants and thus also animals that depend on the native plants, such as the huge number of bee species that exclusively pollinate/feed from specific native plants.

Without a cotton farm, that area could potentially be a forest or natural field instead, which would be far and away better for carbon sequestration, maintaining biodiversity, and conservation.