What Carl is asking for is impractical in the hog business.
Sure it would be better for the hogs to give birth in open pens but they'd need a LOT more space to do so just like it would be better to raise cattle in open pastures rather than feedlots but they'd need a LOT more space to do so.
Meat prices would be significantly higher if something like this was enforced in the livestock business.
An alternative to open pens would be a requirement that hogs are let out of their crates at least 15 minutes every day. We used to have hogs in crates & let them out to eat/drink every day but when we switched to confinement barns, the hogs were kept in the crates until the pigs were weaned. Hogs could only stand up & lay back down with no/minimal forward movement. I agree this is hard on the animals. Hogs required more laxative to keep from getting constipated and after their first birth, they didn't want to go back in the barn for their next birth.
***Grew up on a farm with cattle, hogs, grain, etc...