Because we have systematically degraded the trades until no one is now left to go into them and there is nowhere to learn them.

Over the last 30-50 years we have taught the children of the US that people who work in trades are dumb, backwards, castoffs of society. Its been framed as an unrefined uncultured way to succeed. People tried to make it seem that it was low pay and little to gain.

Many mid educational institutions (mid and high schools) geared towards trades have been phased out and shut down.

With the exception a few around the state and even less in other states. When I moved to CA from CT there were none here at all.