Threadripper having 32 cores is just because of how their dies are setup. I believe they use 4 - 8core CCXs tied together. I know the older Threadripper used 4core dies. My understanding is vague so take it all with a grain of salt and my numbers/ccxs aren't all 100%.
Intel makes monolithic dies meaning they have to make 1 single die with 28 cores that are all working. If any cores fail, they make it a 26 core and so forth. So all 28 core Intel CPUs are expensive and I expect anything bigger is pushing their fabs.
AMD just makes multiple 4/8 core dies and the failure rate of such small dies is lower along with cheaper production costs since they can just tie them together to scale from 4 core CPUs to 32/64 server chips all using the same process leading to cheaper CPUs with more cores.
32 cores is just how it adds up given it's in increments of 4 or 8.