I'm not going to deny that that might be true in some US states' laws. But it is not true morally or philosophically. From the first sentence of the Wikipedia article on wage theft:

Wage theft is the failing to pay wages or provide employee benefits owed to an employee by contract or law.

Later in the same paragraph, it includes as an example:

not paying annual leave or holiday entitlements

It is pretty uncontroversial that not paying overtime bonus rates is wage theft, and that article goes to great lengths to describe how misclassification (e.g. classing someone as a contractor when they are in fact a direct employee) is wage theft not just philosophically, but at times in the US legally.

Here in Australia, a classic example of wage theft that we hear about companies getting fined for a lot is failure to pay superannuation. A US equivalent to that might be if they failed to pay into a 401k contribution match when their employment contract stated they would. It's not "wage" per se, but it is part of the agreed compensation for work.

Leave entitlements are no different. Whether the law recognises it correctly or not, taking away people's annual leave is wage theft.