Just anecdotal history - some guy commented earlier today that my blather is unreadable, so in the name of tl;dr, my point:
When Jobs switched the Mac to Intel, he worked out some sort of deal with Gates to allow Windows to work on the Mac, in hopes it would hasten Microsoft software migration to the OSX platform. Cheers, more beers!
Now to the background blather:
Just an intuitive guess, but I think that the ability to install Windows in a "blessed" manner on a Mac came about around the time Mac migrated to the Intel platform back around 2006. When the Mac went to Intel, it made it possible for users, especially developers, to use the Mac hardware platform directly in getting native Windows software, especially Office, migrated to OSX. A temporary side effect, not anticipated by Apple, was that Linux kernel developers figured out how to get Linux to install on the Mac Intel platform. Apple made no profit on that, so came up with ways to only allow "blessed" OS software to successfully boot on Macs. There was a brief period of a couple of years, around 2007/2008, where Macs produced could not be booted to Linux, regardless of boot loader reconfigurations to get multi/dual boot to work. I installed a boot loader called "rEFInd" to get Linux Mint installed on my old 2006 MBP (1,1), the first MBP on the Intel chip. I tried to use the same procedure to get it to install on a 2008 MBP owned by a friend to no avail. There was some sort of hardware firewall put into the Macs for a couple of years to absolutely prevent any system other than "blessed" Windows to boot. Apple removed the hardware firewall (can't remember the name of the chip) after a couple years, as it cost more than it was worth just to prohibit a few Linux geeks from messing with MacBooks.