Overstaying a visa isn't even illegal and extremely difficult to enforce, and working informally is trivial and pretty much impossible to enforce in a country where citizens don't have to carry ID (sometimes even to vote). Anyone 100+ miles into the country on a tourist visa is basically home free, probably even for life and triply so if they speak English and look European.
So what the US does is put the meanest scariest motherfuckers around in CBP/HSI at the border and then say whatever they need to turn the crank, which does little to someone who knows what's happening but great at scaring a naive German woman who doesn't realize border officers are basically playing a confidence game.
The fact that courts are slow is a problem unto itself that should be solved independently.
Second, I disagree with your stance on strict enforcement without discretion, this often lead to unjust outcomes. Laws exist to serve justice, not just to be enforced blindly.
Third, addressing your "ignorance of the law" argument, sure it may not be a defense, but the expectation that everyone fully understands a convoluted legal system is unreasonable.