I guess you're too young to remember the videos of an AMD CPU (Athlon) getting hot enough to fry eggs the moment a heatsink is removed.
For years, AMD survived as a cheaper solution to Intel. They got competitive with Opteron (and invented x86-64), while Intel was trying to wring out the last drops out of Netburst.
Then Intel Core came out and Opteron got back to being a cheaper but slower solution.