How do you design processors / microprocessor [ not broad ]
If you take out all the complicated things like pipelines, then no it's not particularly complicated and you can do a reasonable 8 bit cpu in a few hundred lines of Verilog.

The pipelining, branch prediction, prefetch, cache etc is what gives designers the speed increases, and what consumes the development effort and chip area.

(Chip tapeout isn't entirely automated in the same way as software compilation, so going from Verilog to silicon involves quite a bit of configuring and hinting the tools to achieve good results at 28nm. Especially timing closure.)

Edit: have a browse of OpenCores OpenRisc design where you can get a feel for how much Verilog is required for a fully useful modern design.