[chronid]

I think there's a bit of "they could" but also something that is considered very little in many contexts unless you have experienced the contrary: integration is costly and integrating properly sometimes is more work than doing something from "scratch", so you don't do it and then you have a mess that hurts you in the long run.

[getoffmyyawn]

I'm sure it's indeed something like that. I think it also comes down to, at least partly, having a culture that is more about building components than systems. I suspect it could also be the "buzz" factor. The press release about building a new system always seems more exciting than one about solving a familiar problem with boring old existing software.