Not only that, but there are a greater number of stadiums nowadays that have some sort of a roof (fixed or retractable) than existed in those days. Below are the current stadiums with a roof:
- Allegiant Stadium for the Las Vegas Raiders (for obvious reasons)
- AT&T Stadium
- Ceaser's Superdome (Saints)
- Ford Field (Lions)
- Lucas Oil Stadium (Colts)
- Falcons Stadium
- NRG Stadium (Texans)
- SoFi Stadium (LA for not sure why considering it's Los Angeles)
- State Farm Stadium (Arizona)
- US Bank Stadium
The biggest reasons that the Cowboys had to practice outdoors then was because Texas Stadium still was exposed to the elements, and the Cardinals were in our division and played at Sun Devil Stadium. The vast majority of outdoor stadiums are either in cold environments or are in places such as Florida and California. Is the OP suggesting that they practice in Antarctica?