The word missing from this discussion is "structural" - there are deep structural changes to how the job market and economy now works that limit the economic prospects of millennials (as a group) in ways that can't readily be overcome with thriftiness and hard work. Here's an excerpt of the article that really clarified this for me: "Thirty years ago, she says, you could walk into any hotel in America and everyone in…
The specific example you bring up seems to be a result of increased liability on the employer for employees. Hotels etc would rather contractors carry those liabilities, especially I imagine when it comes to possibly illegal immigrants.
Shifting all the "liability" onto workers, creating an economy where everyone but the wealthiest are fungible serfs, is a specific set of values and decisions advanced by these people because it benefits them.