> people who use these “second brain” knowledge systems spend more time writing about using them, then actually using them.

All people is far too strong of a claim I think, though if you'd said (or in fact mean) many I might agree.

Is systems attract people who feel they need a better system surprising though? Or is it surprising we hear most from those who go on to spend much of their time talking about systems?

I think there are many who have and use a second brain effectively, but perhaps most don't know that term.