I mean, yes for personal accounts with a couple of thousand transactions - sure. But esp. in payments or in exchanges there can be accounts with millions of tra

I mean, yes for personal accounts with a couple of thousand transactions - sure. But esp. in payments or in exchanges there can be accounts with millions of transactions a day. So you get a double-whammy - those are hot-accounts which also slow down the system, recalculating the balance for those accounts each time a transaction happens isn't an option