Much better quality steel not necessarily thicker. I buy a lot of autobody sheet metal, the stuff I was getting at the autobody supply store would rust in no time, it was so bad the little curly bits made by the shears would rust in a day or 2.
Then I went to sheet metal fab shop and bought it there, holy cow what a difference, I threw a small uncoated piece outside and it only had minor surface rust after 3 months.
The cost is almost double for the good stuff but the repair will outlive the car.
I see some OE pipes still going (albeit rusty but not through) at almost 20 years, the walker is finished in 3-5 under the same conditions.