If you're on concrete with shoes or boots that have threads and your feet sweat, you are a fair conductor to ground through them. But you need a complete path to get shocked. Now put your gloves, jacket, whatever is soaked with sweat on the metal you are welding or table or filler. A new path to ground. You will feel it. Promise.

I would not want to be welding while leaning on an aluminum john boat with no jacket and shoes. All the jumping around, the welds would look pretty bad.