Money and power. It lets companies squeeze more cash out of their customers over time and it lets them make whatever changes they want to something people have

Money and power. It lets companies squeeze more cash out of their customers over time and it lets them make whatever changes they want to something people have already paid for, leaves the door open for things like continuously collecting their user's personal data, and can help make it more difficult for users to migrate away from their product. It's terrible for users who value their money, security, and privacy, but vastly more profitable for companies so most companies will offer it increasingly leaving users with fewer options for anything else.