If Americans would like people to have proper access to healthcare, they would not make it dependent on having a job and make it a universal right funded by the government, but they don't.
I actually am an advocate for higher wages for all, and more government subsidy of healthcare, education, and access to daycare / pre-school; but we can't leave achieving these to whims of each business or the largesse of billionaires.
Americans recently elected a president who enacted tax cuts that benefit Jeff Bezos and the wealthier segment of society, at the expense of government programs that could benefit the poor, the homeless, and the children in need of care.
Also, from a purely business viewpoint: Walmart employs drastically more customer-facing retail employees compared to Amazon thus (1) their morale and behavior has a direct impact on the immediate customer experience (2) the training costs (hence the cost of replacement) is higher due to the need to train soft-skills and customer-facing skills etc. Amazon does pay hard-to-replace employees way above minimum wage, including software engineering, marketing jobs, automation, managers, etc.