The Lisa was a good machine, but there was one big problem. Motorola had come out with the M68000, but not the MMU for it. 680x0 MMUs were years late, and the first one was terrible. The Lisa had a real OS, and needed an MMU. That had to be built out of smaller parts, which increased the cost enormously.

There was also a major bug in the M68000 - instruction backout didn't work. That was fixed in the 68010. But on the 68000, a page fault was not handled properly if a register had incrementation set. So the Lisa compiler had to be dumbed down to not use that feature, slowing down execution somewhat.

If Motorola had fixed those problems sooner, the history of personal computing might have been very different. Intel's x86 machines, with their 16 bit address spaces, might have gone nowhere on the desktop.

Hence the cost-reduced Macintosh - no MMU, no memory protection, no CPU dispatcher. Also no hard drive. The original 128K Mac was a flop commercially. Not until memory cost came down and Apple got a hard drive into the product did it sell successfully. The IBM PC had a hard drive earlier, which got them going in business use. The floppy-only Macs were incredibly slow.