this might be affordable for everyone, don't you think?
$30 for t-shirt? Well, that's definitely a bargain for a t-shirt with embroidered design! Affordable probably for US middle-class incomes. But sadly, there are millions of people in the US who live below the poverty level, who buy their cloths at what we call a "dollar store" or more likely, 2nd hand store. Clothing with embroidered designs would not end up there.
I just wish the Inkscape project had the kind of merchandising program where we could put things that people make with Inkscape into the store. Personally, it seems rather silly for the project not to have that ability. There is a store for Inkscape gear (not widely known yet...well, not even announced yet), but it can only sell its own products, with the Inkscape logo on them. But maybe someday?