It doesn't come with manuals because it is considered a trade secret. Commodore had to lay the hardware bare because it wasn't fast enough to program in a high level language nor did the high level languages fully support their hardware, whereas the hardware of today is so fast that nobody thinks anything of it programming it through a driver or a shared object library in a high level language. It's still wrong not to lay the hardware registers and their functionality bare (yes NVIDIA, have you forgotten your SGI roots?)
It takes time to produce useful documentation though.
I've read a discussion in a forum where an AMD employee when questioned if it was possible to have a GPU's FW without DRM (or something like that) his answer was that would probably be a commercial suicide (OK, I'm little tired right now and I'm not recalling all the details of the conversation but I can try to dig it up... ^__^;)
25 years later I bought the real thing.
Most of the assembly and other DATA/POKE stuff is less than relevant nowadays as hardware has improved and a lot of magic is already done in firmware.
The form of "type it in, verify and run; explain mistakes and correct solution" is still didactically valid.
I'm pretty sure there are programming language interpreters out there with simplicity of BASIC, including BASIC itself.
On MS-DOS, you had a variety of commands built in and extensibility via BASIC too. (or more) Programs could be written as batch files. On Unix-like, the primary interface was via shell, csh, ksh or later POSIX. A set of built in commands. If you wanted something more advanced, programming languages and interpreters were easily available, typically pre-installed.
It was the main interface, magic words. We have regressed to pictures now and most extensibility has been hidden, removed and made very indirect.
Hardware doesn't come with programming manuals anymore as it is deemed too complex (yeah right) and expensive. It is be great if your GPU came with a description and software to write and execute shaders, for example. PC with instructions how to programmatically reboot it, start it or access sensors. How to access EFI services. What the machine code looks like. Etc.