Would a manufacturer of automobiles, for instance, be willing to warrant his products against catastrophic failure if he were forced to build his product using materials from sources who refused to make similar guarantees, because the materials from which they manufactured their products offered no guarantees?
No. He'd be insane.
When you write software, you can't guarantee much unless you can be certain that the software used to create it and the software upon which it depends come with the same assurances.
What about liability? ISVs have been playing the blame game for years. They get away with it because their denials are plausible. I doubt this will ever change.