The hatch being open probably didn’t help. But even closed, BTRs are lightly armored troop carriers, not heavily armored combat vehicles. They resist small arms bullets, that’s about it. They’re intended to be cheaper and easier to manufacture, a reliable, mass-produced workhorse troop taxi with a gun on top. As opposed to something like a tank which is expected to get into more intense fights and hopefully survive them to do it again. And is more expensive because of that.

The BTR is not expected to withstand real hits though. Just not its job.