Not just land and water use, but there may be market reasons, as well as reasons relating to consistency and application specific variations, too.

A bad grow season means lowered supply, higher global cotton prices, etc. Natural farming means lots of supply at harvest, money spent on storage and dwindling supply during the off seasons. There’s often transport costs (usually), and there’s always cleaning and deseeding, too.

On the environment front, while polyester and other plastic-based fibers have their uses, they are often used instead of cotton due to cost. Consumers are becoming more aware of micro plastics, and may start changing buying habits as a result. It’s also possible that governments may start to regulate artificial fibers, too.

Technology-wise, it may be possible to tweak the fibers for specific use cases. It may even be possible to grow colored fibers, or fibers with enhanced strength.

A lab-grown option, especially if at scale, can mean a constant supply of fibers near looms that are customizable, need less post-processing, and are more appealing to consumers.