This is a philosophical issue.
In Intel's view... providing components that exceed the (15W, 28W, ...) thermal envelope when used at max capability is more efficient and meets more use case scenarios than the alternative of only providing a CPU and GPU that together would never exceed xW of power. I happen to agree with that philosophy.
Additionally you could say the same for any given tablet computer design. using a SoC or combination of CPU GPU and other components that all together at max load may exceed the thermal envelope of the case/heat transfer capacity yields a system that is more powerful and meets more use cases than a system that is built with the constraint to always live under a specific thermal ceiling.
This is the current state of modern computer design. Every Intel laptop has the same parts to work with and if you really look you'll find most if not all throttle because they know the math and tradeoffs as well. To make a device which doesn't throttle it has to have a certain size and airflow to dissipate the heat but in the thin and light era they couldn't sell a device that's thick enough or with high velocity fans to move enough air to prevent throttling. Oh by the way same goes for ARM based units.
{trips and falls from soapbox, sprains wrist and ankle, limps to the exit}