I think engineers like to create things. And they will tend, on the whole, to create new things when they have a chance, not because they want to justify their employment, but because they like to do it. And so, if you employ a lot of software engineers, you're going to have a lot of code. Combine that with an incentive structure (likely also created by engineers that like to make new things) which rewards making new things but doesn't particularly reward maintaining old things, and you'll have a lot of new things made, whether it's useful on the scale of the whole organization (something which is very hard to get a good perspective on as an individual contributer, anyway), or not.

I don’t agree with the phrasing, but there is certainly a ton of complexity introduced because of engineers who are trying to be promoted or otherwise maintain their image of being capable of solving complex problems (through complex solutions).

It’s not the same as introducing complexity to keep yourself employed, but the result is the same and so is the cause - incentive structures aren’t aligned at most companies to solve problems simply and move on.

I'd recommend reading bullshit jobs by David graeber. Most jobs in most organisations have an incentive structure for an individual to keep themselves employed rather than to actually solve problems.

I'm not saying it's a conscious impulse! But I've seen this happen more times than I can count.