I think it’s a matter of inertia. Look at oil for instance. For decades, oil companies have made money hand over fist even though people wanted something better it just wasn’t there and it didn’t make a dent in their profits. But now, solar is the cheapest energy we can buy apparently and fully electric car company is a viable business model.
I think it’s a similar situation here. If I wanted to buy durable clothing made out of vegetal materials, I wouldn’t even know where to go. And paying obscene amounts of money for the more expensive stuff just guarantees that I’ll make a statement. The durability of the item will be marginally better than h&m etc but nowhere near the increase in price. And so then, why should anyone not buy the 5$ t-shirt you have to rebuy every year since the 200$ t-shirt doesn’t last 40 times as long?
Same as for energy I believe, when we’ll get credible alternatives then disposable fashion companies won’t make as much money anymore. But the fast that they’re making money now doesn’t necessarily mean people give them their money because it’s what they want... more because it’s all we have.