[Cthulhu_]

Risk mitigation and investment; my employer's software does critical mobile network infrastructure, if they have an outage it affects millions of people. So, if our customers upgrade the software, they want to do their due diligence in their particular use case (it's a flexible system).

That said though, software should be built to allow for fast and painless upgrades. Backwards compatibility and many use cases should be tested automatically and constantly. But, it's a big investment to have software like that, and you need to resist a lot of younger, eager developers that want to e.g. introduce a new language or make sweeping changes.