Reason 1A is probably how few people even have these cards to be discussing it.
 
Reason 1B is just how complicated their behavior is between the GPU boost algorithm, thermals, CUDA core utilization, RT cores, and tensor cores.  
 
For example,  my card with the exact same +120 OC setting will do all of these scenarios-
2130mhz at 45C in timespy
2040mhz at 68C in timespy
2085mhz at 62C in Control with RT and DLSS on
2040mhz at 65C in control with RT and DLSS off
2100mhz at 58C in PUBG (GPU utilization at 60% when around lots of players)
2055mhz at 68C in PUBG (GPU utilization at 90% when alone)
 
So there's no way to say +XXX core setting gets me YYYY clock speeds because there's so many parameters.  An OC that's stable with heavy RT utilization like control or port royal might be unstable in a non-raytraced heavy FP32 synthetic like time spy extreme.  An OC stable in the winter at 18C ambient might be unstable in the summer at 25C.  There's also (and this one is largely my opinion) a lot more sensitivity to PSU quality with the 30 series which is complicating results even further.
 
Trying to write all of those parameters into a single guide that will work for everyone would be pretty difficult.  Even the techtubers are barely touching OCing results on this series.