Replace the BIOS
The biggest obstacle to most generic computers running the Mac operating system on their hardware has to do with UEFI. This system was developed to replace the original BIOS systems that allowed computers to boot up. Apple uses specific extensions to the UEFI not found in most PC hardware. Over the past few years, this has become less of an issue as most systems adopt the new boot mechanisms for the hardware. A good source for lists of known compatible computers and hardware components can be found on the OSx86 Project site.
Lower the Costs
One of the primary reasons people hack the Mac operating system onto generic PC hardware has to do with the cost. Apple is known for high prices for its hardware compared to equivalent Windows systems. Apple’s prices have come down over the years to be closer to many comparably configured Windows systems, but there are still more affordable non-Apple laptops and desktops. Most consumers are less likely to consider hacking a computer system to run the Mac operating systems when affordable alternatives with many of the desired properties are available. Chromebooks are an excellent example of this, as most of these systems can be found for less than half the cost of a basic MacBook.