This "software grows too complex" is certainly a culture issue, and not a software problem. It mostly comes from businesses throwing a bunch of under-skilled labor at the problem, and demanding more and more too quickly. Of course it will outgrow the ability of that team to work with, reason about, keep clean, and extend. They will get frustrated and move on, and a new group comes in, re-writes it from scratch, and s…
They don't get re-written because they can't be re-written without tearing down everything built on top. In every case though there is some newer software out there is inspired by but aiming to "fix" all the short comings of the predecessor.