People are told this because it's generally true. Of course, it's not the case for everyone, but I find that most criticisms of the tool focus heavily on remembering how to use it.
(The author does mention some missing features, which is valid, but git can't be everything for everyone. In those cases, perhaps it's not the appropriate tool.)
> I need to always deeply understand the difference between reset, revert, [...]
> You need to remember that push and pull [...]
> When it comes to merging, you need to think through the logic [...]
Yes, you need to understand, remember, and think. Git (and other similar tools) solve a complex problem and doing so in a simple way would likely restrict teams into a small set of possible workflows.
I find that using git is quite simple once the project team has established the processes where the tool is used, and understands git's role in those processes. In my experience, most day-to-day tasks involve using the same small handful of git subcommands, and issues that arise are quite easily fixable.