David Bradley, one of the original IBM PC's designers is the one who actually invented the key combination. The IBM engineer did the IBM keyboard design and didn't want to create a special button just for this task.
Microsoft needed a way to soft boot PCs and later on to prevent applications from faking the Windows login prompt and stealing windows users’ passwords. David Bradley previously declared in an interview to his defense: "I may have invented it, but Bill made it famous".
But Ctrl-Alt-Del key combo wasn't the only regret Microsoft lately expressed. Current Microsoft CEO Steve Ballmer admitted some mistakes of his own recently. He mainly regretted that in the early 2000s instead of choosing to "redeploy talent to the new device called the phone" they focused all their power around Microsoft's OS "Windows Vista".