I have no doubt that Apple is capable of delivering a product that can beat Intel's i9-13900K, especially since Apple is using a much more modern 5nm process vs Intel's 10nm process for the i9.

As you point out, server CPUs are intentionally engineered for a target market. Apple's processors are very intentionally engineered as well. When engineering their product, they had a certain market in mind, and design and performance trade-offs were made accordingly. As others have noted, power efficiency seems to be a big priority. The M2 Ultra has a TDP of 60W. The i9-13900K has a base consumption of 125W, and draws up to 253W under stress. So do the math. Intel achieves 32% better single-core performance and 41% better multi-core performance (Cinebench) for 422% of Apple's power consumption. If there's something impressive here, it's that Apple is able to do so much with so little. If Apple wanted to, they could probably conjoin two M2 Ultra's and soundly beat the i9-13900K by a considerable margin and still use about half the same power to do so. The real question is why any consumer would need that much compute, and the target market for such a niche is probably very small which is why Apple didn't do that