Intel uses a different socket for the i9-10980XE than they do for the i9-10900. They have done this in the past, it doesn't seem like it is an issue for them to put Extreme Edition (their halo line) into the same naming convention. They don't even make a new tier for it, they just stick it at whatever tier is highest.
You probably don't want the i9-10900X, it's worse in every way except it works on the same socket as other Skylake-X parts. It has the same core count, on mostly an older version of the same architecture, at lower clocks, for higher power consumption, in a more expensive platform than the i9-10900X. In basically every use case, the extra clocks on the i7-10700K even make it superior for multi-threaded tasks despite having 25% less cores.
So there's no simplification here. You can't look at i9-10900X and i7-10700k and go "Bigger numbers better, so simple". You're comparing the worst HEDT CPU to the upper end of consumer CPUs. The only reason to buy it is if you consider you're buying HEDT for the platform (you need the extra PCIe lanes). That information is not in Intel's model names, but AMD put it in theirs, which seems better at explaining that difference (also AMD don't have a third gen 16C/32T threadripper SKU to complete with their own 3950X).