This has been indeed suggested many times but I'll kindly explain:

First off, you never lose gralats at all (except when you purchase stuff of course). Why should there be a bank system when you can own as much gralats at it's fullest limits?

Now let's say this does happen but everytime you die, you will lose about 50 gralats (or something around it)... But wouldn't that benefit player killers more than the players themselves?

Second, if there's going to be a bank system, there should be a trade system aswell. The problem with the trading system though is that it's been heavily discussed upon and no matter how much times you bring it up, there's always going to be flaws to each suggested trade system

and Third, wouldn't the bank be better off as a quest of stopping the baddies who robbed the bank? It was actually a suggested quest idea similar to the York town pyrat quest but it wasn't considered upon and left to the dust