80186 Was not IBM PC compatible. It had e.g. a PIC, DMA and timer built-in, and these were incompatible with the chips in a 8086 based IBM PC.

There were a few new instructions, too, mostly closing holes. You could left or right shift with a constant, while the 8086 had only 1 or the CX register. I think mul also gained a constant.

The fact that Intel released a CPU that could not be put in a PC probably indicates how low they estimated the survivability of the PC.