A piezo based fuse in the nose is an easy way to construct the fuse. It's also easy to construct a safety for it: stick a cap to protect the piezo from getting hit.
That said, the safety cap doesn't help if you accidentally trip and fall after taking the cap off. Most western single use AT designs use a different safety that deactivates on firing.
Is there a reason for this to be a common design for RPGs? If it turns out everyone is using statistical armor, shouldn't RPG designers "catch up" by redesigning them to trigger when any part of the tip is collapsed, instead of just the tip, thus defeating this entire category of defense?