Those systems where the computer equivalent of hotrodding [automotive].
While there remain the same (or even larger) population of people who are willing to figure out how each part of the device works, the vast majority of users are simply satisfied to drive.
This does not necessarily indicate that computer tinkering is any less of a draw. One needs to also consider that the percentage of people who now have computers, in one form or another, has gone from 5 percent of the population to nearly 100 percent of the population.
The 'fun' is lost in the statistical noise rather than being in the center of the distribution.
Another factor is demographics. When I see people pine for the Atari, Commodore, TI99A, Spectrum, etc., it needs to be noted that those where part of the lives of a specific generation(s) of user. As those users matured they lost the desire (not the ability) to continue the adventure. Once inside knowledge and skills have declined older users tend to lean toward nostalgia and the good old days that never really existed.
The manuals for your hardware and chips are available from manufacturers. There is no reason why one couldn't continue your explorations.
A.I. is the new 'hotrod'.