Because, ultimately, the majority of the people working in these shops are not the morally-neutral mercenaries that you make them out to be. Most of them will work there because that is where the work is.
Everyone does have a choice as to where they work, providing there are actually any jobs to support them. But more often than not, there aren't enough jobs for that, otherwise lots of people wouldn't be doing the jobs that they do. Look at MG Rover- I'm sure a large number of them would have rather not worked for a company that has, for a long time, been rather shaky. However, they did because that is where the work was. Now with their demise, by your logic, they can merely jump ship and go and work at another car company. This assumes that there is another similar industry nearby that will take up the extra market at the same rates and with the same need for staffing. As in MG Rover, this is hardly the case, given the amount of automation and importing that is done.
A little empathy is always nice on a wet Friday morn.