Why do they complain about traction when they put on bald tires in the first place?
Those tires aren't bald -- there's plenty of rubber there. They just don't have the tread patterns that street tires do for channeling rainwater.
On smooth dry pavement, those tread patterns are unnecessary, and in fact reduce the contact area between tire and pavement (and therefore traction).
The tires used on those race cars are ideal for the conditions.
Now, if they ever get rid of rain delays and just keep racing, then a different tread would be needed.
Tony Stewart and Jeff Gordon had a little post-race sheetmetal nuzzle on pit road last year, IIRC.