Not a question of marketing to..question of retail space costs at B&M..( waaaaay too expensive to set up a "bespoke" box retail outlet..even on line due to EU postal rates ) and MS threatening any supplier/ manufacturer, who they deal with who also offers linux..
Some "mom and pop" shops do build "bare machines"..but the shipping rates mean that they don't / can't sell outside of their immediate area..
Most linux users ( moi, par example ;) build our own boxen..from scratch..even the ones that we are going to use windows on..
Try shopping ( even on line, in EU or maybe even the USA ? ) for a laptop that isn't preloaded with either windows or mac..