That's because modern CPUs are thermally limited, so they are essentially designed to stay at their maximum temperature and regulate speed and voltage very quickly in order to achieve that.

I've not had as much experience with AMD CPUs, but have seen several times where the stock Intel cooler's mounting mechanism either wasn't fully latched from the beginning or worked itself loose over time, such that the heatsink was never in contact with the CPU, and the computer continued to operate normally, albeit much slower than it should --- sometimes for years --- with the CPU sitting at its maximum temperature and throttling all the time.