>I guess my default answer is: because I have to solve some business problem to get paid, and I never have enough information or time to do it right

That's a red herring.

People working on a business program don't need to encode the "whole information to do it right" (e.g. for the eventual version of the program when every constraint is known).

Just the ones that have to hold at the time they right it, and they already know those -- from their current requirements.

>or phrased differently: If I took enough time to do it right, someone else would have already done it wrong and moved on.

That's also a red herring, unless you don't write tests either.