The problem is that it is a tradeoff on driver safety. A gravel trap negates the advantage of going off track, but in turn it is less effective at slowing a car down in case of an accident, and so it leads to higher impact speeds.
I have always wondered if there could be a little strip of gravel next to the track and then switch back the tarmac. It would keep drivers from dipping their toes off the track and still provide the safety of a tarmac run off.
I wonder if it would be better to put speed bumps like they do on chicanes in some tracks to negate the advantage, they could be positioned in an orientation so that the car is unlikely to go over them when running off track but will if going wider for the corner 🤔