Traditional business models rely on monopoly, and profits for development efforts are directly related to how long they retain that monopoly. They can charge more for software that is unlikely to be duplicated quickly by competitors.

GPL precludes the monopoly business model by requiring any software project incorporating GPL code to also be GPL, thus relinquishing the monopoly.

This is the default price of GPL code, and thus why most businesses regard the GPL as anathema. It makes their business of selling software less profitable, and opens them up to lawsuits if someone, somewhere uses unlicensed code.

They can try to licence the code under more compatible terms, but this is often impractical/impossible/too expensive if the GPL code has many contributors, and

This means the businesses that make use of GPL software have to base their business plans on sources of income that are not dependent on their software monopoly: by charging for their services, instead of their products.

They then only make money when they are actually working, instead of making residual income from selling copies of their completed work.

Businesses that depend on their software monopoly, thus consider GPL to be anti-business.