I understand that a heter iska is basically a method of restructuring a loan as an investment, done in such a way that the lender/investor is more-or-less guaranteed to get his capital back, plus a share of the profits.
So it's relatively easy to see how this works if the borrower is going to be using the money to start (or expand) a business or the like. How, though, does it work for other types of transactions - whether secured loans such as home mortgages or car loans, or unsecured ones such as credit cards? There too, the lender wants some return on his investment. (Or maybe indeed it can't be made to work in a halachically acceptable manner, and then indeed a Jew would be forbidden to take out one of these kinds of loans from a Jewish-owned bank.)
(The question is really more about how things are done in Israel. I assume it's a non-issue in chutz la'aretz, where most of the financial institutions are owned and managed by non-Jews and there's therefore no problem with outright ribbis.)