I think the fundamental problem is that if you do this consistently enough the enemy will assume their AT warhead will be detonated just off the hull by some kind of screen, which if I understand high explosive antitank physics (think RPG) correctly can actually be... better for penetrating armor (a HEAT warhead creates a super heated concentrated jet and a bit of space for it to form isn't necessarily bad depending on details) .

It becomes a psychological thing too I think.

related links

In general, one can expect cage armor or RPG screens to turn only some incoming rounds into duds, or otherwise prevent the explosive from forming a proper shaped-charge jet. If that works, even an RPG full of technically “detonated” explosives that splatter against the vehicle in glops and bang/burn, probably isn’t going to do much damage. Preventing a properly formed shaped charge jet involves a lot of specific science, math, and engineering; suffice to say that there are a number of approaches, and that this is a popular field for additional research.

The offense is also busy, of course. New RPG designs are introducing 2-stage tandem warheads, whose 1-2 punch makes many attempts at passive defense much more difficult. Meanwhile, cage armors will continue to be a popular defensive option against the most prevalent single-warhead RPG threats.

https://www.defenseindustrydaily.com/baes-lrod-cage-armor-03473/

https://www.reddit.com/r/tanks/comments/1cdiduq/if_heat_weapons_are_more_effectively_when/

https://www.mdpi.com/2076-3417/12/10/5064