The driver's are sitting ducks in FI and Indy style open wheel cars from flying debris. They could make it safer for drivers by having a cage protecting them, but then the cars wouldn't look as sexy.
They do make changes, ten years ago, after Canadian Greg Moore died at the 1999 Marlboro 500 at the Auto Club Speedway (then California Speedway) of Southern California, they changed the all grass infields to prevent the kind of skidding that Greg died as a result of.
In 1999, Auto Club Speedway was in the process of being sold from Penske Motorsports to International Speedway Corporation, which reacted quickly to his fatal crash. Following similar changes at ISC's Daytona International Speedway in 1984 (on the Turn 4 side) and 1995 (on the backstretch) and Talladega Superspeedway in 1995 (start-finish line section) and 1998 (Turn 2 and Turn 4), ISC paved over the backstretch infield at both Auto Club and Michigan.