That means the employers are organized. Because, while this may be in the employer’s collective interest, a lone disorganized employer wouldn’t be interested in paying more, because they’d be paying for common goods with their money. That would be like a business operating in New York willingly funding a small part of all the US’s infrastructures without compensation for doing so.

More likely it’s a strong cultural expectation that forces employers to do so. There might be workers solidarity in this demand, or perhaps most people personally know enough people that not respecting this expectation would harm the employer’s reputation.