basically intel took too long getting to the next die shrink. they also failed to appreciate the advantage of amd's chiplet design (or couldn't pivot fast enough to do something similar). both of these allow amd to make more viable parts out of a single wafer, which means they can profitably sell more powerful CPUs at the same price.

it's worth noting that Intel still has faster individual cores (but only because they can clock higher). amd can sell you many more (slightly slower) cores for the money.