The Ottomans basically controlled about half of what the Romans controlled, but it was much more valuable because of all that Indian Ocean trade you remember from last week. So all this land brought a lot of wealth, but it needed to be ruled. The Ottomans could have followed the Roman model, where you send out generals and nobles to rule over conquered territories, or they could have demanded the allegiance of client kings like the Persians, or developed a civil service system like the Chinese. But instead, they created an entirely new ruling class, a system that some historians call the slave aristocracy. So if you're a king, one of your main problems is hereditary nobles, because they always want to replace you, and they don't want to give you your money, and they want their ugly sons to marry your gorgeous daughters, etc. One way to deal with this problem is to make them part of the government so they feel included and shut up. Another way is to kill them.