First, I want to say that this is an excellent question.

The planter class did this because the antebellum South was the ideal location for the production of textiles that could be used by the South, the North, and even other countries (there was business with England for a while). It was easy to plant and harvest cotton because the white planter class used and exploited enslaved individuals for free labor. The dependency of this labor and the profits from selling textiles was such a big deal to the white sellers and business owners, that if something were to get in their way, a majority of them would be unified (physically or sentimentally) in preserving their power.

Here is a speech from a southern Democrat named James Hammond. In it, he brags about the power cotton has over the South; although he suggested the South could reduce how much it plants, he also argued that an attack on this crop (and in turn, textiles) would be harmful outside the South. The "cotton is king" concept only furthered the power-hungry feeling of the planter class, especially in the years closer to the Civil War.

There is a lot more that could be said about this topic, including how the earliest presidents didn't put a cap on textile production from enslaved people doing all of the labor for free (probably because some of those early presidents owned enslaved individuals) or how the South was behind on industrialization and further relied on plantations for their profit-yielding goods. I don't have any sources off the top of my head to look into those ideas, but maybe someone else will expand on that.