That makes two SJs I know know that love reading and discussing books. When I have gone to the homes of many SJs however, I have seen something very neat and devoid of paper and books (which will help it to remain so). I was surprised with my ESTJ to have a lot in common as far as literature (we both loved classics) and he was a high school English teacher, so there definitely is a stereotype that isn't always accurate.
I agree with your statement:
I think most people IRL are just not as interested i nbooks or anything that requires too much thought, due to various ways society is set up to (mal)function nowadays.
When SJs read though, what are they paying the most attention to? If most of the thought process is already decided on what you think about something, you would not be debating and discussing with yourself or others whether you agree or disagree or changing your mind/assimilating would you? So how do you interact with it instead? Is it more a process of gathering information when you aren't sure about something, or confirming something you already believed?
I don't think the SJs are shallow. It seems to me more that there is a lot going on inside sometimes that they aren't even wishing to look at (because vulnerability is uncomfortable), so it is unlikely that others will ever get to see it.