They like to produce complexity, else they get bored while writing the code. But they don't like OTHER developer's complexity.

There’s a crude expression about smells and feces that applies here.

I used to struggle to understand why other people didn’t like using all the clever abstractions I came up with. I felt unappreciated and thought I needed to learn how to communicate better. It turns out I was communicating just fine. What I needed to learn was how to accept feedback.

"If I had more time I would have written a shorter letter" (Pascal, apparently).

Yeah they (including younger me) loved abstractions and complexity I wrote or I read about.

But it’s complex and difficult to grasp, so it’s not fun when you have to get into someone else’s mind, or even to get back into your own thinking after period of a sense of that project/architecture

Most new software devs go through that phase. A few decades ago, it was about the Gang of 4 design patterns. We were all reading that book and then looking for every possible place we could implement those patterns, even when they made absolutely no sense.

I'm so sorry for the teams I worked with in those days. The worse is I felt the folks around me were worse devs for not doing the same. It's so embarassing in hindsight.

The rule is "K.I.S.S (and add more RAM !!!)"