I know it's an isekai trope, but it always seems a bit silly to me when an isekai MC revolutionizes an economy on the basis that no one there thought of some simple idea (like producing a product they easily could, instead of importing it).
Usually it's something like "wow, all this time we were boiling plain meat, instead of adding these spices that grow all around us all the time!", and this isn't quite that bad, but still...I think it's a common fantasy people have that if they visited a "primitive" civilization, they could astound everyone with their common sense from a modern society. But people have been innovative and opportunistic for all of history. The limitations were generally things like not having adequate logistics, not having precise machining, things like that--things you can't solve just by having an idea. Things that need to be built up over time through mutually-reinforcing developments.
Even something like introducing the Haber process would be difficult, since it requires well-designed pressure vessels. It's hard to think of a revolutionary idea or technology you could introduce to some fantasy isekai without running into problems with dependencies. These things always seem to rely on the population of the fantasy world being steadfastly uncurious.
One of the worst examples I can think of was in "Realist Hero" where the MC made the bold and brilliant suggestion that people should eat the traditional foods of their region instead of literally starving to death due to a lack of food imports. And everyone was like "oh wow, what a genius!" Like...seriously...people would be eating whatever they could at that point. The only way the MC is a genius is if everyone else is an idiot.
It's just something I see a lot in isekai without much justification. I guess at least here it's framed as something where the nobles are in control and are happy with the current system, but...even so, a situation like this with the fabric must have been going on for a long time. But the reputation of the Virgo family would only have been suffering for about 15 years, right? So what's the excuse before then, that they would have ignored such a potentially lucrative economic sector?
It's hard to write a world that actually makes sense.