Because anyone interested enough in this topic to do any cursory research -- as opposed to just being an insufferable fedora on the internet -- will realize it's not limited to just one company.
It's very easy and very free to oppose human trafficking in porn by not visiting the websites. Not to mention the personal gains from squashing the habit of seeing human bodies as objects to use for one's personal pleasure. It's significantly harder to oppose human trafficking in construction, what am I gonna do, not enter buildings? Comparing numbers is irrelevant.
Now do you have any numbers to justify that it's, for example, more common than in construction work?