I carry significant amounts of cash when travelling because: my banks are local to one area, I don't use interstate banks (because most of the big ones are crime syndicates), nobody takes travellers' checks any more, and credit cards can be unexpectedly "denied" for spurious reasons. This is actually pretty normal among seasoned travellers now. I wouldn't usually have as much as this fellow, but it's a completely reasonable amount to have if you expect to have to do things like make a deposit on an apartment or an office without a local checkbook.
I don't think it should have been confiscated but it is not a reasonable amount.
As far as your local banks......haven't you ever heard of ATM'S? You don't need a local checkbook to write a check. Also wire transfers for large amounts, I do that all the time. You don't have to bank with a local bank either. You can bank online. You can even deposit checks online with many banks. Credit Cards, always carry a couple, never had one denied but if it were the other Credit Card is a backup.