By at least the 1200's and into the Ottoman Empire, they had become widely used as a tax shelter and way to preserve wealth within a family despite the danger of falling out of favor with the various regimes. In particular, the endowments needed someone to manage them, and it was common to simple name your descendants waqf managers with generous personal allowances. Because of this, by the early 1800's, huge percentages of Middle Eastern wealth were tied up in these endowments, one reason why the financial difficulties of the Ottoman state did not mean the empire as a whole was impoverished. Because of this, both the imperial government and Egypt, which was functionally autonomous began finding ways to take control of waqf revenue.
This is historical context for this article about awqaf in the modern world:
Over the past few decades, as Middle Eastern populations have grown and the Gulf’s oil industry has boomed, awqaf have amassed a vast array of assets, from real estate to cash holdings, equities and even valuable books.
But the management of these assets has failed to keep up with their expansion; money is often tied up in property or bank deposits that earn miniscule or even zero returns, analysts of the industry say. That imposes a heavy economic cost on a region which is struggling to boost private sector growth...
There is little data on the extent to which endowments’ returns lag professionally managed funds, because the vast majority of awqaf do not disclose full financial figures. But since awqaf have traditionally been run mainly by administrators rather than return-maximizing investment managers, the underperformance is believed to be considerable.
There are signs this situation will change, however, as professional investment firms, sensing a business opportunity and encouraged by the growth of Islamic finance during the global credit crisis, offer their services to awqaf - in some cases with the encouragement of governments which want to energize the sector.