In terms of testing, building some setup harnesses for FK data shouldn't be too hard. It's also reuseable work, so that doesn't seem to be a valid argument for anything other than laziness.

However, if orphaned data isn't an issue for the business, then it isn't. If customers can re-enter information, and it doesn't impact business, then it's inefficient, but not wrong.

I'd argue the FKs prevent issues, and I've seen that in most applications, but potentially it isn't an issue, or less of an issue, than the application reporting errors to users. If that's the case, I'd make sure I had queries and checks written to look for orphaned or semi-lost data so I could find it if someone raises an issue.