The reason why the two types of banks had such different views towards their depositors' money was firmly due to the different methods of their remuneration distribution.
The traditional banks guaranteed the money of their clients and even promised a fixed return no matter what. So in return, they were free to do whatever they wanted, spending the money is any investments they saw fit.
The Islamic banks however did not make such strong promises, instead offering a type of profit and loss sharing deal.
Hence just like shareholders were allowed to vote on any decision the company makes, the clients were allowed to get involved in the investing functions of the bank.
This difference in their operations can be further understood by looking at the following example-
Imagine one day you go to a trusted friend of yours and give him 10,000 dollars worth of jewelry for safekeeping… for whatever reason.