that's what a warranty is for...
A warranty can be worthless for a number of reasons (fine print, issuer went out of business, etc.).
These liquid siding jobs involve big bucks. $10,000, $15,000, or more.
If a homeowner finds flaws, bubbling, rotting wood, and realizes their "lifetime paint job" is really a nightmare, they're going to seek redress.
If they don't get satisfaction from the seller (who may, for example, be out of business), they're going to continue to look. And that could take them to the subcontractor.
In an employer-employee relationship, the employer bears full responsibility for the actions (or failures) of his employees. It's not so clear-cut in a contractor-subcontractor relationship. And a contractor may try to shirk responsibility by laying blame on the subcontractor for failing to have properly done something.
Even if a sub can legally escape responsibility, it might require spending quite a few bucks on legal fees.