The problem is, for construction, trades and what remains of agriculture the competition is brutal. It's a low-skill job in terms of prior required education which means there is a looooot of people without degrees flooding into that market already, and then comes immigration that's further driving the wages down because (again) it's work that doesn't require much education or language skills.

I've done a stint in construction (I think y'all call it "civil engineering", aka digging trenches and moving soil) myself, it was rare to find Germans - most of my colleagues came from Eastern Europe.