To properly phrase your example, yes it is depend on "work", but work is dependent on revenue. If McDs needs 10 employees per shift where they generate $800, each employees total cost per shift cannot be more than $80, which works out to about $10 CTC (cost-to-company) per hour in an 8-hour shift.
If you now mandate that the worker salary MUST be $12 or higher than $12, McDs is losing money. So you either pray for an increase in business (sales), or cut costs (ie, fire people) and automate.
And lower-skilled jobs are easier to automate. It's easier to automate fast-food checkout by having (for example) iPads for people to place their orders, so your human workforce can just be the cooks at the back and the janitorial staff.