It can also happen for skilled craft professions. It takes time to train people in that stuff, and if there's been a prolonged period of reduced investment in domestic manufacturing we might genuinely not have enough. Sometimes not having key people like welders, electricians, skilled plumbers, etc. can hold up a project since other things depend on those things.
You could argue that it still ultimately is a wage shortage, but even if the wages are high it takes time to train.
It will take a while for the US to rebuild domestic manufacturing capacity and talent base, but we can do it.