why are you

?
scaling depends on CPU, ie # of cores (typically 2,4,8 ... or 56 if you have a Intel® Xeon® Platinum 9282 Processor

)
and # of threads per core (which is one or two)
-t is generally equal to core number ... on some cpu's you might get better performance for -t equal to 2 x core number.
This is Ryzen 7 2700 (8 cores 16 threads)
I understand that -t is the number of threads.
The question is why the speed increases, but time does not decrease, more often it even increases.