It is not as simple as. First of all even if islamic banks allow landlords to wait until the properties are rented, the waiting time is not indefinite, and is usually limited by 6 to 8 months.

Second: most of the properties are not constructed using bank loans, remember 80% of the properties are in hands of 8-10 people.

Third: lots of empty properties, like villas are simply unrentable. While 5-6 bedroom villa is ok by arab standards (separate living areas for men and women, big families with lots of children), they are an overkill by western standards. Nobody in his sane mind will look for a 4-5 bedroom villa for a family of three. True, many expats live in such villas, but only if companies provide them with this type of accomodation, and even then half of the house will stay locked.

So what's the reason in constructing a palace, investing huge sums of money and then not being able to rent it out? Landlords simply don't have a clue on market requirements, and they are: 2-3 bedroom villas and apartments.

Fourth issue is the quality of workmanship. Brand new houses and apartments are poorly constructed, with uneven walls, breaking pipes etc. I understand that to build them cheaply they export unskilled labour from India, Nepal etc. And these people work as good as they can, but since neither workers were properly trained, nor they countrymen engineers haven't seen anything better, the outcome is miserable. Of course they build it to the best standards known to them, but these standards are extremely low.

There are exceptions, but you have to pay dearly to live in a decent place.