Predictability is the oil that makes nearly every software business run efficiently and smoothly. It affects everything from software development to product roadmap to financial efficiency and profitability. Startups need to know if they have the ability to implement critical functionality before they're out of runway; big companies need to be able to coordinate product development, contracts, delivery dates, product launches across many disparate teams with interconnecting dependencies. Even deciding whether or not something is a roadmap priority requires some concept of how quickly you can implement it.
So yes, productivity theater, as it exists in many project management processes today is unnecessary overhead and wasted time/money. But unless you are id software in the late 90s—flush with cash and sitting on a couple of products that only you can bring to market—you can't rely on "it'll be done when it's done" or "you'll know when it's ready when you see it" and expect to remain competitive for long.
EDIT: Mobile typos.