For one, it doesn't assume pace is consistent. Tracking velocity is part of the game too and it can vary with capacity, talent and maturity.
Secondly, telling business that we can't estimate accurately is more useful than saying we can estimate accurately and being wrong (which is guaranteed). It's a tough sell but it's necessary.
Agree on the second point. I tried to convince some managers and sales guys to stop giving estimates at all and build trust otherwise, didn't work :)
As for consistent, my point was if you have 100 SP in backlog, delivered 50, then I contend you are not in the mid-point of the project. This is a dangerous assumption. You don't know where you are in my experience.
It is if you're following agile principles. By the time you've completed a few stories you should be delivering every feature at production quality with all the automation pipeline and deployments ready. The question from that point is always did we build enough features for a launch.
