I think it's easy to blame others, but programmers are optimistic by nature and bad at estimating. Also, I think all of us have had the opposite scenario where a request comes in from a business-minded person that they think will take forever and it turns out to be trivial. It feels great to do a lot of good very quickly, independent of what the project schedule says.
When these groups hear the words "Agile Development" which was a common buzzword in recently past years - they take it literally - "moving quickly."
I completely agree, and it is often the cause of absolutely unnecessary bugs, stress, inefficient code, and developers often precipitate this bad obsession. But it comes from, and is ingrained from, somewhere else.