Here's another question or two:
If everyone stopped buying clothes from (taking two as an example) Primark & M&S & those companies when bust (not a crazy notion, M&S were in dire straights not so long ago) what would the 50,000 or so employees do? They're mostly low skilled so it's not like they can go into a trade.
If ALL the companies in your list pulled out of whatever countries their products were made in, what would those employees do? Low paid or not, it's got to be better than starving to death in the street. Bear in mind when you answer that one that we're talking millions of people & not just a few thousand.
There's already a situation in the UK now where people are having to choose between food & heating, what are THEY supposed to do if the price of clothes goes up by (let's say) 300%?