In the early days they had to - all the hardware was non-standard. Where would one get 36 bit memory cards? Where would one get CPUs which had a Lisp-specific instruction set? In those early days the computer (refrigerator size) would sit in a machine room (with enough power) and the user would be in his/her room with only a console (plus maybe a second monitor), keyboard and mouse - connected via a long console cable to the machine in the machine room. That was the experience for the programmer/user. The machine itself could have a lot of peripherals: network, tape drive, memory boards, color boards, frame grabber, disk drives, cpu accelerator, ... the programmer would see the driver code.
At some point in time they produced cards for the SUN VMEBus and for the Mac Nubus. Then the only thing left was the keyboard.
So, I agree, the Lisp Machine concept was a combination of Hard- and Software. The emulators of today only provide some of the software parts...
Yeah I have here the book published by the folks who do did the Linn Rekursiv computer, which is sorta like the same philosophy as the Lisp Machine but for a highly object oriented system. Tagged memory, hardware supported garbage collection, object-structured memory, etc. I believe it was also positioned as a VMEbus card, etc.
My understanding is Moore's law just ended up making these attempts uneconomical. By the time HW eng and manufacturing is done on the custom components, "orthodox" general MPU capabilities end up leapfrogging it and a well engineered software VM can outperform.
Maybe we could start to see this change again, who knows.
Maybe unikernels running highly tuned VMs on the hypervisor could be this generation's equivalent. Full control over the MMU, tagged pointers all the way down... hmmmmm
Symbolics could have built computers with custom hardware. At some point in time the 64bit RISC CPUs (MIPS, Alpha, SPARC, POWER, x86-64, ...) were all powerful enough to run Lisp. Genera got ported to the DEC Alpha). They would have been also powerful enough to run Lisp as an OS. But that would also mean writing device drivers, interfaces to hardware and a lot of other stuff. It would have cost substantial amounts of money to port Genera to the metal. Who would have bought that? The idea of a high-level language running as an OS on the metal did not have any future. I don't think there are good examples where this was successful on the market.
At some point in time they produced cards for the SUN VMEBus and for the Mac Nubus. Then the only thing left was the keyboard.
So, I agree, the Lisp Machine concept was a combination of Hard- and Software. The emulators of today only provide some of the software parts...