http latency wild variance on localhost

Running on MBP M1 with 10 cores. Running 1 thread client (wrk) and 1 thread server (java). A youtube is also running on the system. Load average 2 out of 10. Except GC, which could be the reasons of the wild variance in latency below?

"percentile": 0,
			"latency_in_microseconds": 10
		},
		{
			"percentile": 50,
			"latency_in_microseconds": 16
		},
		{
			"percentile": 99,
			"latency_in_microseconds": 51
		},
		{
			"percentile": 99.9,
			"latency_in_microseconds": 1500
		},
		{
			"percentile": 99.99,
			"latency_in_microseconds": 9598
		},
		{
			"percentile": 99.999,
			"latency_in_microseconds": 15021
		}

The same variance happens when using nginx, or a rust web server. The same on the M1, in a Linux docker, or on a Linux EC2 machine. What could cause such a huge variation from 10 microseconds to 15 milliseconds? Thanks