I think that the point is that if those practices are for most employment places in a domain (i.e. the bad practices need not be done by "most companies", just the largest ones) and people's main concern is having to eat, they don't generally have the time to look for the jobs where this shit doesn't happen and even if they do, they would be competing for a small number of jobs against everybody else also looking for those jobs.
Or putting things in another way, your idea that somebody can simply "only go for the good jobs" fails at two levels:
At an individual level, in the absence of clear upfront information about which jobs are good, people who are between jobs and getting squeezed by high money outflows with no inflows (i.e. the one's genuinelly concerned about their "need to eat"), can only search for and be demanding about the quality of the jobs they apply for until they get to the point were they just have to take whatever job they can before they run out of savings.
At a systemic level, if everybody is going for the few good jobs, there won't be enough jobs for everybody. Now in an ideal world were people could hold on for a good job as long as it took - i.e. if people weren't pressed by the need to eat - the bad jobs would dissapear (because they would never find any takers) and all jobs would become good jobs. Once again "people need to eat" means that idea of yours won't work at a systemic level.
Your idea to "exclude from consideration companies that do this" only works for some people, not all people, and only those people who have enough savings or low enough money outflows to not have to concede defeat and take one of those not so great jobs because they're running out of money.
So the previous poster's comment of "we need to eat" neatly encapsulates in a simple sentence the reason why your idea won't work as a general practice or even as an individual practice for most people in the present day society and economy in most countries.