Software release dates are so arbitrary though. We no longer make physical media that needs time to make and ship. Why does software need to be released on February 15th instead of March 7th?
> Why does software need to be released on February 15th instead of March 7th?
Because it has to be released at some point, and without picking a point in advance, you can never reach it.
You could ask the same question about the contents of the release. Why does software need to be released with features X, Y, and Z on March 7th when it could be released with features X and Y on February 15th?
It's inevitable that work will slip. That doesn't necessarily mean the release will slip. Sometimes you actually need the thing, but often the work is something you want to include in the release but don't absolutely have to. Then you can decide which tradeoff you prefer, delaying the release or reducing its scope.