Rabbits are apt to do silly wabbity things, like chew bars from the outside or from the inside of a cage that’s always open. Why they do this is still not fully understood by us mere humans. It could be that they just always want to take the shortest distance route to whatever target spot they’ve picked.
It is however best to try and stop them, for the very reason you give, they can hurt their teeth by chewing on metal bars. Even if chipped rabbit teeth grow out quickly, they can grow out wonky (all the teeth in the mouth don’t grow at the same rate), which can cause chewing problems down the line.
When my bun chewed at metal bars I wove apple and willow twigs through the bars to distract her from the metal. It worked great. I couldn’t block her view of her perceived target (it’s a gate that leads from the veranda out into the garden), but I would’ve probably gone with that option first if it’d been possible. Out of sight, out of mind really does seem to apply to rabbits.