> basics of bash scripting…
Bash alone has a million footguns. If you know to use shellcheck you can probably survive those, and if you read the bash manual in its entirety you’ll almost certainly be well on your way to greatness, but getting devs to read docs – let alone boring, Web1.0 docs, is stretch.
> basics of SQL…
Have you seen the knobs Postgres and MySQL have to turn? Do you know what they all do, when you should turn them, and by how much?
The documentation for both of these is enormous and highly detailed, yet in no way covers everything that can and will go wrong. You only find those things out by using it day in and day out.
As to SQL itself, “I can do inner joins” is about as complex as I’ve seen most devs do. Hell, mention a semijoin and you’ll get blank stares.
I think in general, you’re grossly overestimating the average developer’s knowledge breadth and desire to learn these things. They simply do not matter for most, because tooling exists such that most of the time, they don’t need to know. I consider myself decent at Linux and RDBMS, but that’s mostly because I genuinely enjoy both, play with them in my off-time, and have been running Linux in some form or fashion for the last 20+ years. Also, of course, my work specializations (SRE —> DBRE) have helped.