Because it's better to fix a problem rather than rule around it. Drivers will always try to get as close to the line as possible (literally in this case) so change the tracks to allow them to go harder or to make it too costly to risk.
Also people don't like races to be decided by penalties because it seems too arbitrary and isn't as exciting. Fix the track, improve the experience!
Making the penalty isn't going to do anything when the punishment is handed out laps later when the driver doesn't even know which corner they went off at. The best way to enforce track limits is with a physical barrier, be that kerb, grass or armco. I think Hamilton wasn't getting any track limit violations until they moved the track in and effectively got rid of any physical barrier. When it's just a white line you can't see and you go over my millimetres, there's no way to know you're within limits unless you drastically reduce the amount you push, something only Max could really get away with.
The best way to enforce track limits is with a physical barrier
Or we can stop acting like we're living in the last century and put technology in place that exists already. Helmets can be fitted with HUDs and sensors can be installed on the cars and at corners which need policing. With processing power that exists in current embedded systems, a virtual representation of track limits to an extremely accurate degree can be projected onto the visor in real time.
We’ve had walls for millennias. Way simpler than AR visors and holographic lines.
Maybe horseback riding is more for you?
Walls mean a track becomes deadly for motorcycle racing. F1 is supposed to be at the forefront of technology anyway and spin-offs of such tech could be used in real cars when driving in misty conditions.
Fair enough, then we don't race on moto gp tracks as we agree it's too dangerous for them. There's plenty of tracks where they don't get out of the lines because it's either slower or your race is done if you go over. Lines and penalties don't work no matter what we argue here. Every single driver will tell you they want a physical limit not a theoretical one. The problem is track design not driver visibility. They go out by centimeters at worse, that's not the kind of thing an AR visor will fix.