They run at GHz frequencies, and are orders of magnitude more complex than the 8-bit processors of yore. ICEs were big suckers, and they cost a great deal.
That was for linear-socket, Sub-MHz-clocked, 8-bit processors, like the 8085.
Other tools made it irrelevant, like boundary scanning on the JTAG bus, the EJTAG interface of the MIPS CPUs, the ETM of ARM chips, and so on. The required adapters are still somewhat pricey, but there are cost-effective solutions for both HW and SW.
