I was just making a comment, I understand your premise. Why would a bank want to make a loan they don't make anything on? So what if they don't tap the world of Muslim finance. If they don't make anything they don't give a damn.
The bank does make money on the loan, but it's not structured as interest.
For example, you buy $100,000 house and get a mortgage from the bank. The bank owns the house. You pay the bank $1000/month for 15 years. Each month, part of the $1000 goes towards interest and part towards principal. Over the 15 years, you pay $180,000. At the end of 15 years, you own the house.
In the Muslim version, the bank owns the $100,000 house and sells it to the homeowner for a premium at $180,000. The bank breaks it up into equal payments so that the homeowner pays $1000/month for 15 years. At the end the homeowner has paid $180,000 just like in the traditional mortgage and the bank has made $80,000. But in this case, the $1000/month was all for principal.
It's essentially the same, but the second way can satisfy the religious requirement. You could argue that it's arbitrary and silly, but that can be said about almost all religious customs and requirements--meatless Fridays, disabling oven lights, avoiding interest, etc.
In fact, did you know that McDonald's added Filet-o-Fish to attract Catholic customers? They didn't want Friday sales to go down. I wonder what would happen today if they added a traditionally Muslim dish to their menu like a halal quarter pounder?