Suppose it takes an IQ of about 115 to study at the college level for a B.A., so that only 15% of the population qualifies. The careers you suggested are reasonable for people with IQ of say 100-115, but they DO require smarts that not everyone has. Do you think someone with IQ of 85 can become an electrician? After people stop pretending that everyone is smart enough to go to college, the next step is to stop pretending that everyone is smart enough for the skilled trades. Many people cannot be trained to find jobs paying much above the minimum wage.
Suppose it takes an IQ of 95 or so to be a plumber or a welder. Roughly 2/3 of the population would be able to do a job like these.
Your claim that most people can't be trained to do better than minimum-wage jobs is false. Waiters and waitresses earn more than minimum wage. Factory jobs (mailing rooms, manufacturing, etc.) pay more than minimum wage. But we've outsourced many of these jobs. The other side of the education/jobs coin in the United States is that we think it's a good idea for corporations to put too much emphasis on profits and too little emphasis on the people who help them make those profits.